All too often the PC ATX power supply is neglected. Remember the whole machine is dependent on the power supply. For that reason it’s foolish to buy a crappy power supply.

EC 60320 C14 standard

We spent a lot of money on power supplies until we finally bought the Corsair TX850V2 which has delivered a level of quality far beyond the mainstream. We strongly recommend using enthusiast grade power supplies for the simple reason is that they will last longer.

The consequence is that when an upgrade is desired, the PSU is overloaded and fails. The original PC came with a paltry 65W power supply with a measly 2A of 12V current. Top of the line gaming power supplies now feature over 100A of 12V current.

All power supplies from the original IBM PC onward all use the IEC 60320 C14 standard power connector to the AC power network. IEC 60320 C14 is rated for standard 15A service at 115V and 10A service at 220V. The IEC connector allows the power cable to vary for local markets. Japan is 100V, US is 115V and the EU is 230V but everyone can use the IEC 60320 C14 to the local power service.

The original IBM 5150 PC power supply used a connector that was prone to incorrect attachment. The connector was in 2 parts which led to the confusion. Incorrect connections resulted in a burned out machine. Given the high cost of computers, motivation for change was strong

ATX provided lower costs of assembly as well as allowing for increased integration. ATX also replaced the power supply with a far better design that included keyed connectors to prevent incorrect connections. The I/O shield plate provided enough room for a huge diversity of interfaces. Today the ATX format continues to be very widely used.


The original PC power supply used 5V and 12V bipolar circuits. Only until very recently has the -5V (pin 20, white) finally been dropped. -5V was part of the now long obsolete ISA slot. PCI onwards use single supply logic.

Today the video card typically is the biggest consumer of power in a gaming oriented PC. Top model cards can use upwards of 200W per card. The most demanding card known wants 500 W per card.


Most of the power cables in a PC use 18AWG wire however the smaller floppy cable is 20AWG. 18AWG is safe up to about 5 A which is the defacto standard. To provide more power, PCI Express chose to use multiple 18AWG wires as opposed to 14AWG which can carry more than 30A.

The original PC used color coded cabling for 5V (red) and 12V (yellow) etc. and this has continued as standard. When 3.3V was introduced with the ATX standard, a new color was selected (orange) so that it would be distinctive. As the CPU voltage requirement fell, Intel and AMD both designed regulators for their systems. Modern designs have very sophisticated switching for fine voltage control.


At the back side of the standard ATX the offset screw mounts for the PSU are designed for a 86 mm by 150 mm case. This affords room for an 80mm fan which originally was enough for 350W power supplies.

The standard ATX PSU is 140 mm deep. Our Corsair CS450M uses a 120mm fan that seems to be almost unnecessary due to its extreme efficiency.

Orange+3.3 V113+3.3 VOrange
+3.3 V senseBrown
Orange+3.3 V214−12 VBlue
Red+5 V416Power onGreen
Red+5 V618GroundBlack
GreyPower good820ReservedN/C
Purple+5 V standby921+5 VRed
Yellow+12 V1022+5 VRed
Yellow+12 V1123+5 VRed
Orange+3.3 V1224GroundBlack

Our Corsair TX850V2 is 160mm deep which the modern standard. This affords room for more efficient 140mm fans. The Carbide 300R mounts the PSU on the bottom where the length of the PSU becomes irrelevant. Some extreme power supplies may be 180 mm or even 230 mm deep. An older chassis may have issues, but our Corsair Carbide 300R can mount even the larger models easily for dual video card systems. The 300R also has room below the motherboard tray to make cable management a breeze.


The current motherboard connector is an extension to the original ATX 2×10 connector. The 2×12 connector adds one each of 3.3V, 5V and 12V. Its possible but to use an older 2×10 power supply on a 2×12 connector but that does not solve the problem of an inadequate PSU. PSU failures can destroy other components if they short out.


With the growth in the use of 12V power by the CPU and the GPU, the 2×12 connector is now largely inadequate. The problem is the design was simply to add more power for a single PCI Express x16 slot which is designed to use a maximum of 65W of power.

Many recent power supplies have a split 2×12 connector so that it can be used with an older machine. They are keyed to prevent misalignment.

Gaming oriented motherboards often have several PCI Express x16 slots. The latest models now offer triple x16 slots to support full bandwidth for a three-way video card rig. Some boards come with 7 PCI Express slots allowing flexibility in arranging video cards.

Most contemporary gaming machines use a single video card. Other PCI Express x1 slots are now slowly replacing the old PCI slot however many devices long ago migrated to USB.

The range of integrated peripherals is another consumer of power. USB, Audio and Ethernet are most common. RAM is another consumer of power and recent Intel boards with 6 slots are now common.

Clearly the current ATX PSU is grossly inadequate for modern motherboards that have 2 or more PCI Express x16 slots. Its likely a revision will be needed to increase the number of 12V lines. At least 6 more 12V lines are needed given the trend to more x16 slots. Add-in cards generally now have regulators on them as modern semiconductors use far less voltage than the original PC needed. Some boards have mounted Molex connectors to provide more power to the slots.

Given each pin is capable of about 5A of current, the 5 lines for 5V can provide 25A of current which is enough for a lot of USB ports. The 3 lines for 3.3V can provide about 15A and the pair of 12V lines have about 10A. In total; the PSU needs about 225W to supply the ATX 2×12 connector.



The first 5.25 inch floppy disk drive, the Shugart SA400, introduced in August 1976 used the AMP MATE-N-LOK connector part number 350211-1. That connector was then used by floppy drives and hard disks etc. until finally the SATA power was introduced. The Molex today is largely used for chassis fans. Some front panel peripherals may have a Molex connector such as fan controllers.

Our Corsair CS450M PSU came with pair of SATA cables and one Molex cable while our TX850V2 has a single Molex strand and one combination strand in addition to a pair of SATA cables. Looking at the larger capacity models, there is definitely more use of SATA but Molex cables are still present. Splitters and adapters are mass produced for every possible situation.


Molex fans are easily chained into a set so that its easier to connect them to the power supply. One chassis we have uses pairs of 80mm fans which lends itself to the chaining. Some fans have 3-pin connectors to be attached to the motherboard but our M2NBP-VM CSM lacks such headers. Our M5A99FX PRO R2.0 has some headers but it also is limited.

The 80 mm LED fans we use need about 1.3 W each. The 120mm LED fans we use need about 2.4W each. Larger 140mm fans need about 3.5W each. 200mm fans need about 4W each. Larger fans tend to be less noisy however there is much disparity between fan designs. 80mm fans run at 2000-3000rpm, 120mm fans run at 1000-2500rpm and 140mm fans run at 450-1000rpm.

The CPU cooler uses 4-pin PWM motherboard connectors and chassis fans use 3-motherboard connectors. Some motherboards now offer 4-pin PWM chassis fan headers. Low rpm chassis fans are available for low noise applications. Fan controllers and adapters are readily available.


Our old Asus PhysX P1 card requires a Molex power connector. Early PCI Express 4-port USB 3.0 cards also require a Molex power connector. Over time the Molex cable has become the cable of choice for add-in cards that need extra power.


Starting with the Pentium IV series, the motherboard has required much more 12V current then the primary connector could provide.  Adapters are mass produced to connect the ATX 12V to Molex cables. The old ATX12V has given way to the new 8-pin EPS12V. Most modern power supplies support both types for maximum flexibility. Some extreme motherboards have dual EPS12V connectors.

You must attach the ATX12V/EPS12V power connector or the motherboard will not boot. The CPU uses its own regulator to provide the power desired. It also allows for a dynamic voltage control.

ATX12V can be recognized by the yellow 12V lines closest to the release clip. There is no standard color for ATX12V outside the de facto standard yellow for 12V and black for ground.

Given each pin is capable of 5A of current, the 2 yellow wires can provide about 125W of power to the CPU regulator. The 4 yellow wires on the EPS12V can provide about 250W of power. The extra 12 V capacity supplies additional PCIe slots for SLI/CFX.


Video card makers quickly adopted the PCI Express power connectors to support the growing power consumption of extreme systems. Early extreme cards used Molex connectors with much more limited power capacity. 6-pin PCI Express cables exist only because many older high rated power supplies have multiple lower rated 12V rails. The 150W 8-pin cables simplify power distribution considerably.

Many enthusiast video cards have a pair of 6-pin power connectors. More recently we have seen a few cards use a single 8-pin cable such as the R9 270 and GTX 750 Ti. Flagship cards may use a pair of 8-pin cables. PCI Express powered can be recognized by the black ground lines closest to the release clip. There is no standard color for PCI Express power outside the de facto standard yellow for 12V and black for ground.


SATA hard disks use a 22-pin  female SFF-8482 connector for both power and data. Most gaming rigs use separated power and data cables. Serial attached SCSI uses a 29-pin version of SFF-8482 to support more bandwidth with an extra data channel. SATA hard disk lack the pins for the secondary channel but they still work fine. This is how mixed SATA and SAS disks can be used in a server.

SATA power has 3.3V, 5V and 12V however hard disks do not use 3.3V as Molex to SATA adapters do not provide it. The obsolete floppy uses the smaller Berg connector and fans use the Molex connector.

SATA came from the data center where rack mounted servers needed hot plug capacity to be able to replace bad disks. SATA and SAS absorbed old cabling and controllers. Hot plug capability has given rise to the USB dock for SATA disks. Using such an arrangement, backups are a snap.

DVD drives with SATA connectors lagged SATA equipped hard drives. Today it’s easy to purchase SATA DVD/BD drives. It’s far easier to connect a top mounted DVD drive to a distant header with SATA. SATA cables support a longer distance than EIDE and their thin nature makes it far easier to route cables.

SATA cables are available in a wide range of lengths and colors to match any machine’s decorum. Adapters to connect SATA drives to a Molex connector are mass produced. Molex to SATA Y-cables are also widely available.


Today all that really matters is the 12V capacity. Older voltages are perfunctory, they are present mostly for USB power and integrated peripherals etc.


Given the standard DC electrical equation P=VI, its obvious 12V at 5A is far more powerful than 5V.

Most vendors quote maximum capacity of the unit which typically is the sum of the capacity of each circuit. This can overstate the true capacity of the unit. Reading the PSU label will quickly determine the available 12 V current.

Some vendors still use old obsolete designs. The attempt to increase capacity with an additional circuit. Some have several. This adds to the complexity increasing the failure rate. Our defunct AK 680 uses a pair of alleged 20 A circuits that provides the capacity to operate a single gaming card. We have seen some other models with 4+ circuits. Load balancing is vital when using a multi circuit power supply.

Power supplies are available with a single circuit. These obviate the need for load balancing. These power supplies tend to be somewhat more costly only because high power semiconductors are expensive. We have seen models with 60 A and more on a single rail. The Corsair TX850V2 we use achieves 70 A of 12 V on a single circuit which is enough to drive a pair of gaming grade video cards. The more modest CS450M achieves 35.5A in a single 12V circuit.

Its possible to use field effect transistors in parallel and they can be scaled up as desired. Using a DC to DC converter makes it easy to create 3.3 V and 5 V etc. Its a simpler design.


Over current protection (OCP) on a single rail PSU is simpler to design and implement which is more cost effective. It far harder to implement OCP with multiple circuits and load imbalances aggravate the problem. A current limiter is simple to design and they act only when the load exceeds the design threshold.


Over voltage protection (OVP) on a single rail PSU is simpler. Multiple circuits need multiple OVP circuits which add significantly to the overall complexity of the design. Most power supplies use a Zener diode for the reference in the voltage controlled oscillator.

Most power supplies also include a metal oxide varistor to provide transient protection. An simple low pass RF filter is needed filter out the high frequencies used.

Hard disks use a transient voltage suppressor diode and this is often damaged in machine by poor quality power supplies. Once the diode is damaged, the disk fails. This is why its so important to get a quality power supply. Once the hard disk fails, data is lost,so be sure backups are updated and secure. USB disks are OK.


Ripple is AC noise leaking through to the output. Sources include the AC line and the voltage controlled oscillators used in the regulator circuits. To prevent noise being reflected back into the grid modern power supplies now all use a filter on the AC line.



We use Corsair and the quality of the power is extremely good. Noise, transients and ripple are almost nonexistent. This is due to the use of much better parts. Cheap power supplies cut too many corners which can lead to a shorter service life and the specter of burned out components when it fails. We presently use the TX850V2 and the more recent CS450M.

Transients and noise can negatively affect components. A cheap PSU may use cheaper lower temperature 65°C rated capacitors which can fail in a warm gaming machine. The TX850 uses much better 105°C rated capacitors which can take the heat fine. We advocate standards to force all manufacturers to use 105°C capacitors to prevent fires. Fire safety is important. Our TX850 is rated for 850 W at 50°C leaving no room for low quality capacitors. Overheating is the primary cause of PSU failure.

The CS450M is so efficient it hardly is noticeable. The temperature difference from ambient is generally < 1°C. This allows Corsair to reduce costs with lower temperature rated (85°C) components.

Corsair provides 5 years on our TX850V2 which markets the durability. The less expensive CS450M comes with 3 years however it should also last a long time.

ATX is very slack with a 5% tolerance for voltage etc. The negative voltages are allowed 10%. Enthusiast PSUs generally are < 1%.

Overclocking can unbalance the power delivery from the video cards PCIe connectors and from the PCIe bus, drawing maximum power from one source and reducing the maximum overclock you can apply. The single rail design can cope with this easily.


Testing the TX850V2 with the P4400 showed the PSU to have an excellent power factor above 99% at all loads. Power supplies all use a simple low pass filter to prevent RF leaking into the grid. Early switching power supplies had a poor power factor which wasted a lot of power.

The best power supplies use an active power factor correction (PFC) to improve efficiency. This eliminates the need for a switch to select the input power. The TX850V2 is able to tolerate even brownout conditions to an extent. In the heat of the summer a lot of air-conditioners can load the grid rather heavily.

The goal with PFC is to keep the load current and voltage in phase and the reactive power consumption at zero. This enables the most efficient delivery of electrical power from the power company to the consumer. Reactive power flow is needed in an alternating-current transmission system to support the transfer of real power over the network.


The power on self test (POST) usually has every device enabled for a several seconds while the BIOS figures out what is present and then finds the boot device. Once Windows has loaded the drivers then the power load is reduced as devices become idle after enumeration.

For this reason we are adamant not to use a cheap power supply. Over time the stress of POST alone will slowly degrade a marginal model. We like using a PSU with double the needed capacity as this will lead to a much longer service life.



The early designs of ATX power supplies used small 80mm fans at the rear of the unit. Cheap power supplies use low cost fans which can become noisy from dust buildup. Most newer models use a low cost bottom mounted 120mm fan to improve air flow. Our TX850V2 is equipped with a 140mm double ball bearing fan. Our TX850V2 bears many characteristics usually seen in commercial data centers.


Based on the Arrhenius equation, which says that time to failure is a function of e-Ea/kT where Ea = activation energy of the failure mechanism being accelerated, k = Boltzmann’s constant, and T = absolute temperature. The life of an electronic device is directly related to its operating temperature. Each 10°C (18°F) temperature rise reduces component life by 50%. Conversely, each 10°C (18°F) temperature reduction increases component life by 100%. Therefore, it is recommended that computer components be kept as cool as possible (within an acceptable noise level) for maximum reliability, longevity, and return on investment.

In the Carbide 300R the TX850V2 usually is slightly below 29°C with a modest load. Playing games may increase it to 32°C. The lower temperatures can easily double the typical service life of a PSU. This justifies the expense of the new chassis with the bottom mounted PSU.


The new EPA Energy Star 5.0 specifications for computers became effective on July 1, 2009. Starting at 80% real efficiency, the graduated scale established a competitive PSU market. The PSU market is now segmented by the relative efficiency with 80 plus platinum at the top of the market. Competition however will keep prices reasonable.


One aspect of power supplies that is missed by 80 PLUS is the 5V standby power. The goal is to reduce power supply consumption considerably when in the power off state. Many power supplies are very inefficient when in standby or power off..

The One Watt Initiative was launched by the IEA in 1999 to ensure through international cooperation that by 2010 all new appliances sold in the world only use one watt in standby mode. This would reduce CO2 emissions by 50 million tons in the OECD countries alone by 2010; the equivalent to removing 18 million cars from the roads.

Using the sleep key on the keyboard puts our computer into standby and the space bar wakes it. Modern powered USB hubs are on all the time but switching power supplies are comparatively efficient. USB also fully supports device power management. Standby typically needs to have jumpers on the motherboard set to make the 5V standby available to the keyboard.

The cost of standby energy is easily estimated; each watt of continuous standby consumes about 9 kWh of electricity per year and the price per kWh is shown on electricity bills. At $0.11 per kWh it means close to $1 per watt per year for a continuous load. Given the world uses around 2.3TW, the scope for energy savings is stupendous.


The state of California has mandated an even more aggressive ½ watt initiative. The EU has also mandated ½ watt as well.

Looking at power supplies for notebook and tablet computers, none bear the 80 PLUS mark that PC power supplies offer. This is the main motivation that drove the ½ watt initiative given the plethora of power supplies for phones, tablets and notebook machines.;


The 300R chassis has 2 front panel USB 3.0 ports. These use as much as 5x more current as USB 2.0 when configured for BCC charging use by modern phones and tablets. The TX850V2 and CS450M etc. have enough standby current to actually charge a phone without powering the machine. The USB 3.0 ports are provisioned with standby power.


ATX 2×12 motherboard connector225 W
ATX12V CPU (4-pin)125 W
PCI Express 6-pin x2150 W

Most gaming machines use a single video card as shown in the first example. 80 PLUS gold power supplies are now easily available in the competitive entry level market.

ATX 2×12 motherboard connector225 W
EPS12V (8-pin)250 W
PCI Express 6-pin75 W
PCI Express 8-pin150 W

Using a high-end motherboard with more PCI Express slots needs more power even when using a single high end gaming card.

ATX 2×12 motherboard connector225 W
EPS12V250 W
PCI Express 6-pin x4300 W

During the system startup power demand is at its highest. We strongly suggest adding 100+ watts to cover the extra load. Keep in mind that a PSU is more efficient at partial loads.

ATX 2×12 motherboard connector225 W
EPS12V250 W
PCI Express 8-pin x4600 W

Using 2 top grade display adapters can use phenomenal amounts of power. This is where the market for 1200W+ power supplies offers the most efficient models. Typically machines with CFX/SLI using dual GPU cards for a 4-way system.


Enthusiast NVIDIA cards. See our GPU page for background information.

8800 GTX128 CUDA90nm12181Wpair 6-pin
GTX 280240 CUDA65nm14236W6-pin and 8-pin
GTX 285240 CUDA55nm14204W6-pin and 8-pin
GTX 480480 CUDA40nm12250W6-pin and 8-pin
GTX 580512 CUDA40nm12244W6-pin and 8-pin
GTX 6801536 CUDA28nm8195Wpair 6-pin
GTX 7802304 CUDA28nm12250W6-pin and 8-pin
GTX 980 Ti2816 CUDA28nm12250W6-pin and 8-pin
GTX Titan2688 CUDA28nm24250W6-pin and 8-pin
9800 GX2256 CUDA65nm16197W6-pin and 8-pin
GTX 295480 CUDA55nm28289W6-pin and 8-pin
GTX 5901024 CUDA40nm24365Wpair 8-pin
GTX 6903072 CUDA28nm16300Wpair 8-pin
GTX Titan Z5760 CUDA28nm24400Wpair 8-pin
RTX 309010496 CUDA8nm24350W12-pin
HD 59701600 stream40nm8294W6-pin and 8-pin
Sapphire HD 69701536 stream40nm8287W6-pin and 8-pin
HD 79702048 stream28nm12210W6-pin and 8-pin
R9 290X2816 stream28 nm12300W6-pin and 8-pin
R9 290X 8GB2816 stream28nm12330Wpair 8-pin
HD 69903072 stream40nm16375Wpair 8-pin
HD 79904096 stream28nm24400Wpair 8-pin
R9 295 X25632 stream28nm24500Wpair 8-pin

The AMD Radeon HD 6990 has a switch that can change to BIOS2 with a 450W maximum power. The factory ships with the switch in the 375W BIOS1. This has carried on to the HD 7970. This will undoubtedly benefit overclocking. The R9 295 X2 ships with its own water cooler.


One often overlooked area is overclocking. The power requirements above for the video cards are for reference designs only. Overclocked video cards will need proportionally more power. The same for a CPU.

Our Athlon64 X2 is 65W at 2.2GHz and overclocked to 3.025 GHz the device will need about 90W of power. Our Phenom II X4 965 BE is 125W at 3.4 GHz and overclocked to 4GHz it needs 150W of power. Modern motherboards can deliver abundant power but regulators can heat up considerably.

A single GTX 260 needs 182W at 590 MHz and when overclocked to 650 MHz the cards needs closer to 200W of power. The BIOS2 switch on the HD 6990 increased the power draw by 20%.

For this reason we strongly recommend a much larger capacity PSU to allow adequate headroom for overclocking. A weaker PSU with low grade capacitors is much more likely to fail.


GPU bound games games such as Metro 2033 can increase power consumption on a video card by 120% of the TDP as indicated on the vendors web site. For this reason a suitable chassis with adequate fans is needed in addition to a suitable PSU.

Enthusiast grade power supplies are usually rated at 40-50°C. Lower cost models may range from 30-40°C with budget models mostly rated at 30°C. Its advisable to use better rated models when playing games for extended periods of time. We have a digital thermometer attacked to the power supply to be able to monitor real temperatures. We noticed 35°C on warmer days ambient .

AMD and NVIDIA both also support additional power to drive their respective products. The example from the AMD Overdrive shows how 50% power boost can increase performance. Given the 250W card with a 50% boost now makes it effectively 325W.

The amount of power boost only comes into effect when the load is very demanding. This is seen with the leading action shooters such as Battlefield: Hardline or Wolfenstein: The Old Blood. Less demanding classic games Half Life 2 will reduce power consumption due to dynamic power control.


High-end power supplies use modular cables to make cable management easy. A single GTX 260 uses a pair of PCIe 6-pin connectors while the GTX 590 uses a pair of 8-pin connectors. High-end 1200+ watt power supplies are usually well provisioned for all conventional ATX permutations.

The 6/8 pin connectors like the ones on our TX850V2 are the best solution. This way any permutation is supported easily. We have seen video cards with one 6-pin connector and up to three 8-pin connectors.

Modular cables are moving down the price range into the mainstream more quickly. Mass production of cables will make this options more popular over time. Using only the cables needed will also reduce clutter found in many gaming rigs.

Our 80 PLUS gold CS450M is semi-modular. The 2×12 and EPS12V are hardwired. The peripherals are modular which is the best way to reduce cost.


The old ATX standard for a PSU is 150mm W x 86mm H x 140mm D ( 5.9″W x 3.4″H x 5.5″D ). Most power supplies fit this size fine. Some extreme power supplies may be longer and thus intrude deeper into the chassis. There is ample room with ATX and EATX chassis for a bigger PSU.

ATX motherboards are 9″ x 12″ and are standard for gaming machines. EATX is 12″ x 14″ so the space advantage is enormous. Compared to the mid tower ATX most gamers use, the EATX chassis is huge. A single GTX 260 is 10.5″ in length which fits the standard ATX chassis. Some Radeon cards have exceeded 12″ lengths compelling the move to EATX.

Full EATX chassis have the most room for a multi-GPU setup. PCI Express cables are relatively heavy so bending them into shape is easy. Video cards need as much air as they can draw in so its important that the air flow supports this. Cable ties make sure cables remain in place properly.

A modern gaming chassis is well suited to cope with the longer gaming power supplies. Modular cables will use more space. The DVD drive has become shorter allowing even more room so there are lots of options for routing cable sets.

Bottom mounted power supplies are now more common and this arrangement allows for even easier cable management. Wires can be run under the motherboard to keep them away from fans etc. The large space at the is convenient when using longer power supplies. Our Corsair Carbide 300R uses a bottom mounted PSU and this makes it easier to improve air flow.


Looking at power supplies, the most desirable feature is a single 12V circuit with adequate capacity. Careful checking for a suitable PCI Express connector set is vital for gaming grade video cards. Modular cables are desirable and are now more widely available.

Using a PSU with 2x the capacity of the active gaming load will be at the peak of efficiency curve. This is why nothing under 650 W is suitable in a gaming machine, especially if overclocking is desired.

We would be happier if all PCI Express cables were simply 6-8 pin so that 2-way users have adequate resources for dual GPU cards. Providing 6 cables is feasible on a single rail PSU to support 3-way single GPU cards and 2-way dual GPU cards easily. Many 1200 W power supplies still ship with 6-pin connectors. A dual GPU setup in SLI/CFX provides a 4-way machine that can play games on ultra for several years to come.


The latest most extreme PSU yet, now up to 1500W on 115V. 94% efficient which is 80 PLUS titanium. Would be silent with a GTX 660 Ti for games.