The PS4 motherboard must NEVER receive 12V on the standby pin. That will fry the Southbridge instantly.
I've searched for a paper or guide on adapting a PC power supply to a PS4 Fat, and I found a few resources that might be helpful. Keep in mind that modifying a power supply to work with a console can be challenging and potentially hazardous if not done properly. adaptar fuente de pc a ps4 fat