I installed my new EVGA 3080 Ti FTW3 Ultra Gaming card about two months ago without issue. Since then I have experienced several full computer shut downs. By shut down I mean everything suddenly shuts off and then automatically comes back on maybe 3-5 minutes later leading me to think its a fail safe mechanism. 

What leads me to believe its related to the new card (other than the fact that it only started to happen after I installed it) is that it seems to happen when I have a game and another application running at the same time. Let me try to explain. I can have YouTube open on one screen and play games on the other without issue. But when I minimize the game (have it running in the background) and I focus on a web browser, excel file, or discord for a while, the computer will immediately shut down then moment I click to return to the game. 
 
I wondering if anyone else has experienced this and how they might have over come it? Is it eating up too many frames while the game is idle? Is it just a setting that needs to be changed?
 
Any help would be appreciated, thanks!
EVGA GeForce RTX 3080 Ti FTW3 ULTRA

I have a SilverStone 1200W PSU

try not use any splitters on pcie cables each one should have there own dedicated cable.

Complete computer specs would be helpful in trying to diagnose any issues. Especially in cases of complete reboots. 
 
Does your computer blue screen? And if so, what error does it report on it? All things to keep in mind. 
 
So, It's impossible to even attempt to help without full PC specs, and any errors if they exist. My initial feeling is either Memory or PSU issues. Especially driving two monitors, one for the game, and another for web, at the same time.

Check dimm temps
3080 exhausts directly over ram and is 52 degrees in my system (3080)

My ram temps were 55 plus which resulted in shutdowns.

Yeah amd
5800x
Aorus b550 master
Corsair 3200 32 GB rgb ram

Never had a problem with my asus 3070 but that produces a lot less heat (and I never stress tested with PR which requires stable ram)
 
Update: did more testing ram DIMMS is still overheating even with the cooling fan.  On closer inspection, there's a lot of vents from the backplate spewing hot air into the system which I measured to be 53 degrees.  I took some heat sinks and covered up some more of the 3080 exhaust vents and DIMM max is 50 degrees and I'm able to complete PR stress testing at 29 degrees ambient.  Hope this helps.

aka_STEVE_b
Older seasonics have issues with the 30xx series extreme voltage spikes - change your psu /or RMA your current one will probably solve all your problems

+1 ....complete shut down or reboot points to PSU....