I have an AUSUS A8N-SLI deluxs, which also takes a 24 pin Power supply connection. But it runs absolutely fine with my 20pin antec power supply connected. As long as your Power Supply can supply enough amps on the +12V rail, you should have no problems.
Also, the wattage of the PSU doesn't really matter, it's the amps on the +12V rail that make the difference.
My case came with a generic "450W power supply". This supplied only 9A @ 12V, when my setup required closer to 20A.
I bought a "480W Antec True Power" and it supplies 28A @ 12V. More than enough for me.
Moral of the Story: Dont be sucked in. There are so many ways to measure "wattage" that it's not a very reliable indicator of the PSU capabilities. If unsure, buy from a reputable brand. Personally i prefer Antec, but there are plenty of others.