That plug is just power plug. You plug the floppy power plugs from your ATX power and it will chain start this PSU. The issue I have is that sometimes that process takes too long and the GPUs do not start in time for the system to see them.

I have the USB ones with dual relays on two rigs. Mine work fine. I have then set for 120 second timeouts, and also they monitor that the mining script itself is working.