Well... you kind of are. You said that Corsair PSUs are good in America but not UK (they're literally the EXACT SAME PSU regardless of country) and that they're "obviously problematic". You stated that Seasonic makes Corsair's PSU, but then you also stated that Seasonic is better quality than Corsair, which is also incorrect. Obviously wherever your getting your information from is seriously misinformed.look im not here to have debates with people on the internet about Power Supplies
.....And now, here we are, you replaced the PSU and still have a problem.
Just trying to set the record straight.
So, I didn't see where you updated the BIOS. You said you reset it, but do you actually have the newest 7C80v1A BIOS (from last month).
We use MSI boards almost exclusively, and we had a HUGE problem with shutdowns and reboots with Ampere cards (typically 3080 Ti cards now) and EVERY SINGLE MOTHERBOARD had to have a BIOS update in order to make them stable. Now... problem solved.