This could be made with relay and some other circuits but...
Has anyone even seen or know how to make an ATX Power Supply without the use of a motherboard power turn on by pushing a case button. Similarly turn off my pressing that button again.
It may be easiest for be to just replace the push button case switch with a toggle.
More aboutmotherboard case power button
It is possible to turn on a power supply without connecting the 20/24 pin power cable to the motherboard. It is normally done to test the power supply. Is that what you want to do or do you mean something else?
Yes, i'm aware of how to short a PSU to turn on, but i would like to retain the function of my cases power button. As i plan to use this PSU in a case without a motherboard.