Schematics about the R600 power
The R600XT, or Radeon HD 2900 XT needs two power connectors, one 2×3 pin and one 2×4 pin. If your PSU doesn’t have the 2×4 pin one, then you can plug in a 2×3 pin one, but you wont get the full potential of the card.
You need the second 2×4 pin for overclocking, as othwise ATI's Overdrive overclocking utility won't work at its full potential. You can read more about it here.
The card will overclock even without the 2×4 pin connector, but the scores won't be great. We heard that there will be a lot of new PSU's introduced starting Monday. Here is a diagram of how it looks in the real world.
