One of my GPUs is an XFX (I know, I know) 280x. I noticed yesterday evening that the rig it was attached to was off. It wouldn't power on.

Obviously, I suspected the PSU. However, I determined with some troubleshooting that the PSU is fine. If the six pin power plug on the GPU (it has two, the eight seems irrelevant for this problem) is plugged into the PSU, the PSU won't start. If the six pin plug is unplugged, everything (except the GPU, obviously) works normally. If the PSU is already running and I plug in the six pin plug, the PSU immediately shuts down.

I was able to repeat this several times with three different PSUs and the problem occurs even when the GPU is not inserted in a PCIe slot or in the computer at all, and even when using a PSU that literally nothing else is attached to.

I'm guessing internal short of some kind.

Any thoughts? Anything I missed?