Question Need help, PC randomly shuts down.

[popsi1397]

Need help, I've been having this issue since a power outage happened. My pc would turn on and run for hours at a time but then randomly shut down. Sometimes it's up for 2 minutes - 8 hours. Full on turns off No BSOD, no error codes, Event viewer just says The Kernel Power event ID 41 which leads to absolutely nothing.

Things I've done:
- Replaced PSU, since it was a power outage I guessed my PSU was cooked. problem still persisted.
- GPU is okay it ran well and did not overheat at all, I play low requirement games. Heaviest game I play is Elden Ring
- Changed power sources [From a power strip directly to wall]
- Ran memtest, passed
- Ran a CPU stress test didn't turn off
- changed CMOS
- Reassemble the PC [Test benched it on top of mobo box]
- Turned off fast boot [recommended by a friend]

I got a spare motherboard since I'm building a PC for my sister anyway and tested if it would still happen on the new motherboard, It still persisted.
I have brought my PC to a nearby technician as a last resort. Will update regarding that but in the case that they can't fix it what do you think caused this problem? I am at a loss.

PC SPECS
aorus gigabyte b450 pro wifi [old board]
asrock b550m pro se [new board]
ryzen 7 5700x
corsair cx650
asus rx 6600
corsair vengeance 3600 x2 8 gig
samsung 970 evo 1tb