ATX12VO is not implemented into the Z690 chipset based motherboards for Alder Lake. The manufacturers seem to have moved away from it. The standard requires a new compatible PSU with a 12V connector w... Intel Z690 motherboards remain to use 24 pin connector over of ATX12VO
motherboards are busy enough, stupid idea to make them do more than they already do with pcie 4/5 ddr5 memory etc.. I doubt you want voltage conversions circuits on the same board too, probably doesn't help with interferences I don't really know but I had an engineer complain to me he had a 5nA leakage so yeah we're talking extreme sensitivity here that's 0.000000005A lol
Ok. People assembling rigs for themselves replace PSUs pretty rarely. This one will "justify" the price bump. Like if mobos weren't expensive enough. I'd be surprised if an idle phone charger had more leakage.
You will need power cables from motherboard to power your hdd or ssd And rely on motherboard makers to make good quality converters, enough power power ports. This will increase price on motherboards!