Power supply exploded while testing

I was repairing my iMac and removed all the components to replace the thermal paste and I put the power supply and motherboard in so I could test it. I didn’t put any of the screws in and when I plugged it in I heard a explosion. When I looked at the power supply, there where some black marks on the pcb. At the time I didn’t realize that the black padding was conductive. I started troubleshooting it and I found that there was a short on one of the diodes. I desoldered it and I tested it by itself and it was fine. So there must be a short somewhere else on the board. I was wondering what components go bad on the power supply when there is a short and if anyone has any advice on how to fix it.