Normally I would have suspected software or heat causing your issue. But your power supply model is definitely the #1 suspect
https://linustechtips.com/main/topic/515473-teardown-and-review-of-the-turbolink-atx-xg500w-crappy-psu/
Recommendation: Replace that power supply ASAP. Even if you weren't having this problem, I would recommend replacing that power supply. I strongly suspect it's causing your issue though.
Addendum: Despite my recommendation, would you mind uninstalling the drivers with DDU? (
http://www.wagnardmobile.com/forums/viewtopic.php?f=5&t=337 ). Click "Official Download Here". Select to remove the drivers from Safe Mode, when prompted. After the drivers are removed, then download the latest drivers from Nvidia's site.
Then download and run HWMonitor and check the CPU temps during game play. These steps are still worth taking but again, and I recommend that you do them now, however I still think your power supply is what's causing your issue. Please remove and reinstall the drivers in the manner I listed, and also report your CPU temp during game play (play a game that you know results the crashing).