Today many gaming grade motherboards are sold mostly as they are more feature rich compared to the low cost models.
The X470 and X570 motherboards have an additional ATX12V beside the EPS12V connector. This means two cables are needed to supply the motherboard. Some motherboards have dual 8-pin connectors like the TR4 motherboards. Entry level motherboards tend to have just one EPS12V which provides enough power for 95% of users.
The EPS12V power is largely there to feed the CPU regulators. Some of the power is used by the slots and on full ATX motherboards there are usually 6-7 slots depending on the design. Regulators are mostly 90% efficient but new designs are now reaching 92%.
The MSI GX470 Gaming Plus has only 6 slots , the area often used for a PCIe x1 slot is used to support a longer M.2 SSD. The area with PCIe x1 slots has become widely used for M.2 slots and the idea of dual M.2 slots is desirable for cloning to a larger capacity etc. Secondary slots tend to be slower speed. The resale of M.2 SSD drives is subject to the same price declines as new models endure.
Power supplies like the Corsair AX1000i have an extra EPS power cable to that motherboards can be provisioned. The HX1000i has abundant plus to connect all the needed cables.
The old AX860i also has abundant cables for the modern motherboard. The Corsair AXi was the flagship but new models that are less costly to manufacture are replacing them.
To be sure the HX1000i power supply is overkill but the cabling is very desirable. The cables are completely modular so they are easy to place in the channels on the chassis and this reduces the clutter big time. Zip-ties can keep cables together and they can be moved under the motherboard tray where there is room for them.
Swapping the motherboard with cables under the tray means no problems upgrading. The Corsair SPEC-01 has lots of room under the tray for power cables and other components. Corsair generally has about 1 inch of space under the motherboard tray for cables.
Changing a motherboard with managed cables takes 1/3 the time as there is no need to rewire the machine. Once a new board is placed and a few screws are securing it properly, the power and front panel connectors hook up fast.
Igor’s analysis simply the same as I have found with my own tests. Video card power draw can be brutal. This is why NVIDIA recommends a 750W PSU for the RTX 3080 and an 850W PSU for the RTX 3090.
The old post on the ATX Power Supply is still the most comprehensive guide for understanding PC power supplies.