The Dell PSU is a quality part and it can support up to a 150W GPU. The only time it would have an issue is if you used a 6 to 8 pin adapter to run a GPU over 150W. Then the multi rail PSU would probably shut down. The Hd 6850 is listed as a 127W GPU. I'm running a GTX1060 on that same PSU and a 120W X5470 Xeon. Don't worry about it.