PC Needs to Sit Unplugged for 15 Minutes after Shutting Off
So I built a PC about 7 or 8 years ago, and it worked awesome. Still does, with one exception: when it is fully shut down, it won't turn back on until it has sat unplugged for approximately 15 minutes. This issue first came up a year ago, and I was certain it was the GPU after it failed the paperclip test, but when I popped over to Best Buy for a replacement, one of their techs offered to test it for me and it came back normal. I took it home, plugged it in, a voila. Figured at the time it must have been a wonky connection or something.
I rarely fully shutdown my pc, so it was several months before it happened again. This time, I did a bunch of testing and confirmed several things:
It doesn't happen on restart, only full shutdown.
If it happens, I wait 15 minutes, and start it up, I can then shut it down and bring it back up normally right after.
Somtimes it happens on normal shutdown, but it always happens on hard shutdown or if I accidentally kick the power switch on my surge protector.
It is not a fast boot error, as fast boot is off.
It is not a power switch issue, as I replaced the mechanism and had the same error.
There is something wonky about the power switch/its connections, because it has multiple LEDs, and they are sometimes on and sometimes off randomly. Given I've ruled out the assembly, I wonder if it's maybe the pins on the motherboard, but they hold up to visual inspection.
Performance is normal, heat is normal when idling and under load.
At this point, I am wondering about my PSU again, or possibly about my motherboard. Is it possible that one or the other isn't discharging residual charge properly after shutdowns? Any advice would be helpful about where to go next in terms of troubleshooting. I feel I'm out of my depth.