I have a cheap Shimano DH-3D37 which is doing a good job so far. The quality on this hub is not far from the more expensive ones, except the weight! I made myself a simple USB charging device with a rectifier, a couple of electrolytic capacitors and a LM7805 5V regulator. Works just fine that one too. Some might say it's an inferior circuit because it's not a switching regulator with a higher efficiency, but that's not quite true. The regulator will never run smoking hot because the input voltage will always "follow" the output current and hence reduce losses through the LM7805 regulator.