obviously it supplies power. i was under the impression that it takes a/c and converts to d/c for d/c chargers. but at the track i see guys using a charger that could be a/c or d/c using them even when there is power available at the track to just plug into. so i ask, if i use a generator and my chargers will use a/c power, is there any reason to invest in a power supply? are there any other benefits to using a power supply? what am i missing here?