Question I sent my PC to a local repair shop, they said GPU was the issue, shutoff at PSU level still occurs.

Oct 15, 2021
I sent my PC to get fixed by a local repair shop after it started to randomly shut off after a few hours of total idle, and 10-20 minutes with a browser loaded and a few tabs. It was bad, requiring me to turn the PSU switch off and on. They said after running it a couple of hours without my GPU, and that after putting it into another PC, that PC failed to post.

After replacing my GPU, the issue occurred even after using DDU and installing new drivers following the guide, and seems to be even worse, with it shutting down almost immediately after logging in. What would be the most likely issue? And would a faulty GPU cause my PC to shutdown at the PSU/cause another PC to not post?

Twp things to note.
I sent it to them before as my PC wouldn't post, CPU ezdebug light was on, and fans never ramped down, and it was fixed for about a week after they replaced my CPU.
And I had to replace my PSU following a storm, but my PC performed totally fine afterwards, with the exception of me having to reseat the 24 pin due to it being loose(likely happened during my move) until the aforementioned CPU trouble.

My specs are: MSI B450 Tomahawk MAX Motherboard, 2x8 Ripjaws V 3600MHZ RAM, Ryzen 5 5600x CPU, Noctua NH-D15 CPU cooler, Cooler Master MWE 650w Gold Plus PSU, MSI RTX 3060TI GPU(the GPU they said was faulty is a EVGA 2070Super).

Any help would be appreciated, as I'd love to get my PC up and running again, along with knowing whether or not I wasted money ordering a new GPU if my issue couldn't be caused by it.