Power cuts out randomly, have to unplug from wall to reboot

So just the other day, my 2020 iMac screen went black, the power completely cut, and and no amount of holding the power button would get it to come back. I ended up having to unplug it from the wall, and then it would boot up again. This blackout happened a few more times that day, I tried shuffling around/removing RAM sticks and running the diagnostics, but nothing came back with issues or solved the problem. Eventually it stoped crashing, so I backed up some files and kept using it as normal.

Last night it started blacking out again, and now it can’t even get through the boot sequence, and safe boot makes no difference. This has now made me believe that it’s a hardware failure, and not a software issue. The closest thing I could determine is maybe a faulty PSU, but I really wanted to know if there were more rigorous tests I could do before ordering and installing a new one. Does anyone have any other ideas on what could be the problem, and how I could diagnose with more certainty?

Side note: I’m also remembering that I have had an occasional problem with this computer since I bought it (new) where the fans would suddenly spin up to maximum, sometimes even when it was sleeping, and none of the fan control applications I tried would ever actually register the RPMs. Sometimes they’d spin up for 20 seconds, and other times I had to shut down the computer and unplug it from the wall to make them stop. I don’t know enough about the hardware of this computer to make real educated guesses, but misbehaving fans and power management sound somewhat related to the SMC? Could the SMC itself be faulty?

Thanks,

Jak