Seasonic S12 380 is definitely quieter than the Antec SmartPower 2.0. It is also be able to provide enough juice for most PCs. It is obviously not a SLI certified PSU, and install something like a X1900XTX should not even be attempted.
If you want a quiet case and PSU then check out the Antec P150. It comes with a 430w NeoHE PSU that is almost as quiet as the Seasonic. It's selling for under between $110 - $120 before shipping.
Older NeoHE PSUs has had problems with Asus motherboards in general, but was fixed when newer versions were shipped back in February.
Yes, but the P150 is quite expensive...
I'm going to buy SLK3000B + PSU LC Power 550W GP