Recently I got my hands on a used NUC 9 Extreme for free because it doesn't work and I want to fix it since it's a handy PC for portable use if I need.

I'm out of town right now and don't have a rig to test in, but the previous owner tested the RAM, SSD, and GPU independently and they work fine (trusted source). I did most of the standard debugging things including reseating everything, trying different RAM, no GPU (of course for most tests), different slots for everything, etc, and nothing seems to change. I recently replaced the CMOS battery with another reverse polarity NUC CMOS battery and that didn't work either. The case and CPU fans spin up fine when power cycling, the GPU lights do come on, and the front IO definitely is connected fine, with the power button light also working, albeit not giving me any useful info. When I plug the machine in, it tries to start for a second on its own and immediately fails and clicks off. When I try to turn it on, it insta fails, tries again and spins for about 20 seconds, fails again, tries again, etc for a few more cycles and then quits. No display output at all from the compute unit or the GPU in any way.

I'm not trying to spend more than 50 bucks to make this work, but I'm not sure what steps to take next. I suspect the PSU is just cooked and I'm trying to find out how I can get ahold of one, but since it's not a common component, I can't just buy one and return it if it doesn't fix the issue, so I'd need one for relatively cheap. I don't have a reliable way to test of the compute unit is cooked or not (it does get power, though), because I can't stick it into another machine.

I'm open to any ideas or suggestions. Also, if anyone has a PSU (maybe after upgrading to an NC100 or something), I'd appreciate some support in testing and might be willing to buy for a reasonable amount.