A PC draws quite a lot of watts. Even quite modest machines can draw easily a hundred watts on power-up, and stacked machines can need a lot more. If you want to electronically switch that kind of power, you need a relay - a solenoid-activated switch. Of exactly the sort that is not provided on the Just Cooler receiver board. The receiver shown on the box has a couple of relays, but the thing that comes out of the box just has little transistors, without the high voltage and/or current handling you need for high power switching.