Random Power Loss During and After POST

So I’ve been grappling with this issue for a few days. My PC will suddenly shut off under “idle” loads. The system will often boot but can shut off during POST. CPU thermals don’t reach temperatures where I’d expect a shutdown. It does boot for longer if I leave the PC plugged out for a long time.

At this point I’m experimenting with just a single stick of RAM and integrated graphics but I’m still having issues. I’ve tried replacing the CMOS battery, fully resetting CMOS, replacing my thermal paste, reseating everything including the motherboard and I’ve tried using a different PSU to no avail.

Any help would be greatly appreciated!