Does your Gen6 support a heated bed? If so, you need a wall wart which can supply at least 20 Amps at 12V, which is around 240 Watts. If it doesn't have a heated bed, power requirements are a lot lower, around 5 Amps at 12V, which is 60W, which most wall warts can supply. I had a Gen6 from Mendel-parts which had 2 terminals to wire in power, I used a 12V 30A power supply used for LED lighting, sourced cheaply from ebay. Still using it, now with RAMPS, and it has plenty in reserve to power the heated bed. Using an ATX PSU is not ideal, as you need to put a ballast resistor on the 5V power line to keep it enabled, and very often it is not clear how much current each rail of the PSU can supply (the 12V rails are often a bit weak), which is important when attaching a heated bed.
