Cutting the power for 30 seconds drains capacitors. The most likely culprit is in the PSU, but I’ve also seen it be the motherboard or GPU.
Desktop PSUs have been pretty standardized for 25 years. The odds are pretty good that you still have an old one, or know someone that you could borrow from long enough to test.
Failing that, just get one from a place with a decent return policy. I like Micro Center, if you’re near one of those.
It does if you have career progression and promotions in mind. Also if you’re looking for some new insights to shake things up.