It’s logical to think that since the ATX12VO power connector is a cut-down version of the existing 24-pin connector that existing ATX PSUs would be compatible with ATX12VO motherboards using an adapter cable, but it’s more complicated than that. When asked if it would be possible to use a passive adapter cable, Intel responded with the following:
“The main problem with using an existing Multi-Rail ATX power supply to power a new ATX12VO motherboard is the 12V Standby Rail. The existing Multi Rail ATX Power Supplies use a 5VSB rail. This would have to be converted to a 12VSB rail to work with ATX12VO motherboards. The new standby rail of 12V was determined by working with power supply vendors and motherboard manufacturers to determine the best overall efficiency. There were minor efficiency differences between 12VSB and 5VSB. Keeping the new power supplies as 12V/12VSB only was the best option to improve overall power efficiency.”
It sounds like compatibility isn’t totally ruled out, but it won’t be as simple as just hooking up the right pins. PSUs are expected to have a longer span of usefulness than motherboards on average, so this could be an important point if ATX12VO is ever going to win over the DIY community. We reached-out to a power supply engineer at a large company and confirmed that a 5VSB to 12VSB adapter is possible and already exists, because ATX12VO is similar in ways to power supplies that Lenovo, HP, and Dell already have for OEM systems. One could take an HP-to-ATX12V adapter and re-pin it to work with 12VO, for example.
