I was using SATA extensions for the 3 hard disks cages I have installed. Hard disks do not use a lot of power except when the machine is cold started or rebooted The BIOS enumerates all storage devices to find the operating system.
Looking at the PSU it shows 3.3V use as zero. The reason is that modern logic uses 1V or less now due to the very small feature size. The real problem at 3.3V is that losses in power cables is comparatively high. Hard disks use 12V for the motor and 5V for the logic board.
None of the peripheral cards installed use 3.3V. It seems that designs now focus on 12V and 5V. Graphics cards use 12V due to the higher power required. The GaN regulators are offering 92% efficiency and eventually these will find their way into all graphics cards,
The Intel proposal for 12V only is incompatible with the contemporary gaming needs. Many desktop users have USB cables galore to charge up a mobile phone and tablets etc. Of course wall mounted USB chargers are available but iTunes is needed to change music on the iPhone. The machine even has a USB 3.0 card to support more front panel ports. Migration to USB-C is likely to be sluggish given the entrenched USB-A universe.
Given the abundance of SATA power cables and the abundance of peripheral ports on the AX1600i I have now setup two power cables to power the disks with one on an extension as the two cables only amount to 8 connections.
The box has cables from several Corsair power supplies. This provides options for power that assures stable operation. The demise of the old AX860i provided an extra set of cables which has been helpful with the super tower machines.
I have lots of SATA power cables so I could use one per cage which would definitely handle them with an abundance of power. Still using 3 SATA power cables does seem a tad excessive.
Corsair SATA cables all have 4 device connectors as this is the most common scenario in mid-tower chassis. The old Cooler Master HAF 932 has 5 hard disks bays so an extension was more convenient. The HAF 932 needs new feet as the old ones are abraded down to the metal screws.
The Obsidian 750D has more room in it than the typical mid-tower so it can handle larger power supplies and multiple video cards. There is even room for a top mounted water cooler for the CPU. The 750D has ABS plastic feet that seem to be fine with carpet so some consideration for refurbishment of the HAF 932 is needed. Replacement feet for the HAF 932 are US $13 each which is why the Corsair chassis was procured. The 750D can have felt attached for linoleum floors but it appears that the feet do not scuff flooring.
SATA hard disks in Windows are usually powered down unless they are active. This is to reduce overall power consumption as disks can spin up relatively quickly. At present the Toshiba 12TB disk handles the active game collection as it has the workload capability in abundance. Modern TCL and QLC SSD endurance is still available for gaming needs but the capacity of the server class hard disk has some advantages.
Corsair power supplies are good with abundant power which is desirable in gaming. The long service life is also very desirable as high end efficient models are expensive, Corsair is rock solid with warranty when the AX860i stopped working due to the logic board fault a replacement was provided quickly. There are lots of power supplies in the studio along with motherboards and processors etc. Never know when something dies.