295x2 has only two 8-pin power connectors, it can pull 600w from the wall. Single 8+8 pin pcie cable will melt so you need to use two separate 8-pin pcie power cables from Power Supply Unit to Graphics Processing Unit.
Oh so I definitely have to buy a power supply?
Best regards
Edi
You will definitely want to invest in a 850w gold supply minimum for only that gpu. The commentary about dual PCIE power is one born of safety but in my experience it is not necessary. I've been riding a 295x2 for a good little while and with relatively effective tuning you should be able to reduce its power to ~475w at the wall in dual mining mode.
When you're not tuned, it will rip well up to 675w in dual mode.
Hi
cool. Can you tell me which PSU are you using, please.
Also, is the motherboad good enough