So yeah, after successfully hooking up my anycubic kossel to an atx psu, I tried to hook my fusebox2 to the same psu. I took two yellow and black wires from the pcie connector and connect it to my mks gen L. Before turning on the psu I unplug my anycubic. Then I tried to turn on the psu, the lcd lit for a second then the wires start to smoke and the psu shuts down. I checked my board and found my rectifier was broken (S1A code diode). The board survived because it's still on when powered via usb.
Anyone know why the rectifier broke? The voltage was 12v and everything was normal.

I'll post images later if necessary.