As of PSU, in my case I am using server IBM 2880W PSU to power the cards, and my workstation is protected by 6kW online UPS, and I also tried different cables, different PSU, and even replacing motherboard - so I am sure at this point that the issue caused by Nvidia driver.
I did not try to downgrade yet, not sure to what version to downgrade to? I think I tested 550 and 570 proprietary drivers, and now I am testing 575 “open” Nvidia driver without any workarounds applied, so far after 3 days and 3 hours still working well, but only time will tell if it remains to be the case. I will update this thread if I experience the issue again with 575 driver.