I was concerned, too, when I went from an Enermax Whisper 430W PS in my old Antec case, to the new Sonata case with the 380 smart PS.
But I haven't had any problems with it, and it also comes with two "fan only" power plugs that you can use to plug in both 120mm case fans(one comes included, the other 120mm fan you have to add). Using those plugs for the fans keeps the noise level down.
You'll only need to add one 120mm fan, DMF, because the Sonata comes with one already installed. I recommend the Vantec "Stealth" case fan, as it's very quiet.
You're gonna love the Sonata. It's very, very quiet. Best case I've ever owned.