Lots of them aren't real switchers though because they aren't regulated; they basically crappy wallwarts running at a higher frequency and the ripple is probably terrible. I've opened one up once and it was just a transistor oscillator on the mains side with a rectifier, small filtering capacitor and resistor (to provide a minimum load) on the secondary side. The primary and secondary sides were on separate little PCBs and there was no feedback whatsoever. Even though it was rated at 5V the output measured about 8V off load.