i had this problem as well ( drives stoppeds responding, dxrenderer error , shut downs ) and i tried every trick in the book...clean install, driversweeper, older drivers, leaked drivers, re-install dx11 etc etc. The only thing that worked was an RMA. Spare yourself the time and frustration and get a replacement. Trust me. ( make sure the replacement has a different serial number) Once the 7850 works...it rocks!!
Your problem is different.
I'm sure mine is a driver or BIOS issue related to the 2d/3d clock switching, because I have no issues in most games, and the monitor has never blacked out in a game - only with movies, or on desktop with a game in background utilizing 0-2%. Most issues were fixed by raising the 2d clock ...
7850 only draws 130 watts, and only has 1 connector AFAIK.