I bought a second hand Vega 64 (dangerous ex-mining card I know...) the owner told me that the card never had a problem while gaming, so I gave it an oportunity....and finally the card arrived...., and I was quite happy with it. Performance is awesome I undervolted it and the card stays cold at 1000mv p6 and p7 levels with 145w - 190w of power consumption, memory is clocked at 945 mhz ,950mv. Excelent results. The problem appears more and more frequently in a lot of games, the pc suddenly reboots, without any BSOD or messages or nothing. It only happens in certain games, randomly, can happen at the beggining or after 20 minutes, or 5 minutes, is completly random.
My rig :
i7 8700 with Aorus H370 Gaming 3
16gb DDR4 Patriot
Gigabyte RX Vega 64 Gaming OC Dual Fan
Samsung 250gb M2 NVME SSD
CoolerMaster Silent Pro M 1000w
Before this I had the same problem, in my other pc I used to have a i7 3770, with another motherboard, same SSD same PSU and same VideoCard....
Practically different computers, just same PSU and videocard, and the same problem. The last week I bougth a brand new CoolerMaster 750Gold Fully Modular, it didnt solve the problem my pc keeps restarting, but this time with a little "tick" sound like a switch, maybe the PSU is cutting the power or something.
8 pins connectors are connected individually each conector to the PSU not with single cable.
Windows event viewer shows Kernel-Power Critical Error.... with no error description number, the pc reboots so fast that windows does not have the time to log the cause.
The rarest thing here, was that I borrowed the Vega64 to one of my best friends, for like 2 weeks he is a gamer he played ARK and Dota2 really heavy on summer with high temperatures in his pc with a Coolermaster 700w psu without any problems, balanced config, or with undervolting.... even in turbo mode (which is crap config on this gigabyte cards)..... oh my god I DONT UNDERSTAND. 
At my home the problem persists, even in balanced mode, or pretty undervolted. The card works flawesly in terms of performance is really a shame...
