This computer doesn't have an AGP or PCIe video card.
An overclocked i7-4770k with an overclocked GTX 780 will only pull about 350w at max load. The GPU is the most power hungry piece in the computer.
Cpu will pull a max of 80, HDD 15, motherboard 50, CD 15, RAM 20, fans 10. Adds up to 190, and that is theoretical max power consumption. It's very difficult under normal circumstances to pull 100% max load on everything in the PC, which is why I said 150.