Powerbuilding, like strkout said, is a combination of bodybuilding and powerlifting, and the accessory work is geared toward hypertrophy. So you get the good of both worlds.
I may be going into powerbuilding in my off-season, since I want to do some sort of powerlifting routine, but at the same time keep symmetry as much as possible (to compete in figure competitions in the future). I'm still not 100% sure yet what I want to do though.
Perhaps Steve (Bendthebar) or Bodybygamma could chime in with their more thorough knowledge on the subject