FIrst steps would be to identify if chosen PSU might be inadequate for load, such as running a 450 watt marginal no-name PSU with a 2080Ti, etc...(not all PSU's claimed wattage ratings are accurate, and many slap on names like Gold or Platinum but cannot handle even being run at 60-75% load continuous....)
Then you'd want to check the temps of both GPU and CPU under a full /adequate loading of each...(sometimes BIOS settings will authorize a shutoff if certain temps are reached, so search for those settings to disable them so you can at least check /observe temps before a shutdown)
Lastly, some homes power fluctuates enough to cause a partial brownout when central air/heating turn on, or a clothes washer starts up, etc...; if on a UPS, bypass it. If not on a UPS, perhaps you can borrow one of adequate wattage one to see if it helps