Hi,
Hope you doing great, so I 10000% sure is PSU as I have had same spec system except 2080 ti at that time, and my PSU was RM 850 gold it just did not like to play games as I had random restarts, they way I sorted just bought new PSU EVGA supernova 1000w gold and just enjoy my new PSU and my upgraded PC as now I run on EVGA Rtx 3090 FTW3 Ultra V2 and my cpu is OCD 5.3Ghz not to mention as per above 
my cpu is same 11900k and ram same amount 32GB 3600mhz, get new PSU and enjoy your setup