Yes, the lower you set the voltage the lower the power of the pump, it can pump as little as about 250gph and as much as about 1450gph. I don't really have the knowledge of electronics to explain all the details but an AC pump spins at 60Hz or 50Hz whatever is the mains frequency so 3600 or 3000 rpm. A DC pump sets it's own frequency and that is how speed can be adjusted. The maximum wattage will be just under 20W but it is really all the same, it is the wattage the entire unit pulls which doesn't matter whether it is AC or DC. The pump gets DC current but it is running off 115V AC 60Hz that is stepped down and converted by the power supply.