Thank you for all your replies,
I have a Corsair Enthusiast Series 850w TX850http://www.amazon.com/gp/product/B004MYFODS/ref=oh_details_o06_s00_i00?ie=UTF8&psc=1
Will that be enough for two gtx680??
So a friend suggested that if I choose going for SLI, then I would get into a lot of trouble with games compatibility and that there's even a risk some games will have worse performance than with a single card. So he told me to save up the trouble and just sell my gtx680 and go for a gtx780
how big is that risk?
I'm not sure if this is a dumb question, but I'm new to pc and I used to play on consoles before.