Unfortunately, they won't accept it back now that I've replaced the PSU with a custom unit, and the old one is gone (repair shop never gave it back to me..)
I had tried to get in contact with them since I bought it, but apparently they were having issues getting emails from Yahoo accounts, so they never received any of my emails for almost a year, and as such, I've missed my refund period and they won't do a refund/replace. They wouldn't even upgrade the PSU with a unit they owned, even when I offered to pay extra/the difference, because "we can't do upgrades, only replace with the same model".
Honestly, it just feels like I have put in a lot of money (and now even more) as well as a bunch of time, hours a day for almost a year, trying to fix an unsolvable problem.
I appreciate the info, though. Good to know its not consistent with their builds, I just hit the unlucky one.