What loading current can I expect from a hub dynamo for my mobile device?
Most simple charging devices supply no more than 400 to 500mA at their USB-output. Modern devices (such as the USB-Werk) can sometimes deliver more than 800mA (corresponding to 4 watts). However, for such high output powers, a cycling speed (in a 28" wheel) of well over 20 km/h is required, even with efficiently working charging adapters.