Is this a PSU  problem? 

I have a 1000GT, which is only about a year or 2 old, and every now and then, my computer just shuts off. I'd say it happens 1-2 times a week. There are no other issues; everything is fine; it doesn't matter if I'm gaming or just watching a YouTube video. It's just off turns off, and restarts. 
 
No overclock on ram or CPU or GPU.. The computer has been stable since the last time I was having weird issues where the 5900x CPU just randomly died and couldn't hold stock clocks. 

- what do your Windows errors show? (Event Viewer)
 
yes, it could be the PSU or even the wall outlet (momentary power interruption?) 
 
.... though other items in your PC could cause the issue ... I've had a bad hard drive cable cause that kind of issue before

- Is the outlet you are using on a wall switch?


- have you test at another wall outlet?
 
- Are you using a UPS or a power strip?
 
- check all connections to hardware & psu, make sure nothing is loose or not fully seated, including the power cord in back of psu, check all connections between MB & the PC case
 
- what else is connected to your PC?
 
list hardware in your PC & OS /Windows details