Switching is the way most computer power supplies work these days - it has nothing to do with ANY physical switches. There is a web site called HowThingsWork (I think) and you can go there for a good description of a switching power supply - but basically, the AC voltage is rectified and then put through a chopper (high speed solid-state switch) to increase the frequency from 120Hz (the frequency after rectification) to a much higher frequency which is more efficiently handled by the relatively small transformers of these PSUs
.bh.