In my case it had to do with my PSU. I run an 1080ti and 8700k. While my PSU had enough overall watt, the 12v lines were separate. My GPU caused the PSU to crash. Test this: put GPU power on 150% and run Furmark. This caused my PC to instantly crash.
Just wanted t to thank you for your post. I have the same CPU and GPU as you. My PC was rebooting when I played Destiny 2 (usually towards the end of a lengthy strike). Turns out I had my 2x GPU plugs connected to the same rail. Once I had them connected to separate rails each, the problem was fixed.