VR Zone writes NVIDIA's Kepler will be revealed in the week starting March 20th. The site published details on the card's power circuitry, you can check it out over here. It seems the card will have a six-pin and eight-pin power connector, enabling a theoretical max power draw of 300W.
As you can see on the diagram above, the board requires a single six-pin and eight-pin power cables (Theoretical Max: 75W + 150W + 75W from the PCIe connector = 300W) even though it should operate with just two six-pin rails. Then again, if you purchase a performance product, it is expected that you'll have at least a 500W+ PSU where 8-pin connector is the norm.
Three phases are dedicated to feed the GPU (NVVDD-PH2, PH4, PH5), and dual phase is for driving the rest of the board - a couple of gigabytes of GDDR5 memory and 3rd party chips (NVVDD-PH1 and PH3).