Very few UL power adapters are as good as the ones Apple makes. I ran a bunch of my USB charger "cubes" at medium load and looked at their output on my o-scope one time. Most of the UL listed adapters had way more noise than the Apple one, even at just 500mA. There was one other manufacturer's charger that was as good as the Apple charger, but I can't remember off the top of my head who it was... I think it might have been HP or Asus or something.