I just built one using an Antec SL350 20 pin with no problem, using a 20-24 pin adapter. I couldn't use the Raidmax PS that came with the case because the Asus MB manual said it could use a 20 pin IF it supplies at least 15 amps of +12 V. The Raidmax only had 13A even though it was 420W, while the Antec has 21A!
BTW, my Asus temperature probe acts funny - it will read ~100+ degrees when called up for the first time, but every time after it is around 86 degrees, which can't be right. Other than that, it runs very well.
Update on the probe - History looks to be working correctly. The computer seems to idle at a nice low temperature and warms up to about 115 degrees F when running Sims 2.
I guess I'll see if there is a fix on the Asus site.