Can you mix AMD and Nvidia cards on the same PC (when mining of course)?

Also what watt PSU would I need for the (3) 1080tis and the (1) RX480
Running the 1080tis at 80% load only.

I have an EVGA GQ 850 Watt 80 Plus Gold

The Mobo is a ASUS PRIME Z270-AR LGA 1151 and supports Quad SLI