Not sure if this applies to power supply,s that have an on/off switch
yes it does> the main switch doesn't turn on the power, normally when the PSU is in the board the board (UEFI) gives a signal to the PSU and then only it turns on
you can rewire that easy with 2 pin connectors switched together, mostly on the ATX connector its a green and black wire (GND) right to eachother. Shortcut those and the PSU will power up.