What you have there is a "switching power supply". Incoming 60 HZ AC is rectified and filtered to produce a high DC voltage, which is then converted into a high frequency AC by an oscillator (several transistors), and then fed into the primary of a high frequency transformer, and stepped down (or up) to the required level for the load. Most of these supplies then convert the AC back into DC with a rectifier stage, and usually a voltage regulator to ensure stable output. In the case of running a few puck lights, the raw 20 KHz AC is apparently deemed sufficient. [Linked Image] Switching supplies are everywhere today, from PCs to microwave ovens to TV sets. The "electronic ballasts" used for fluorescent lights are specialized forms of switchmode power supplies.

The primary advantage of switching supplies is weight and space savings by eliminating bulky 60 Hz magnetics, and physically large filtering capacitors needed at 60 Hz. Higher overall efficiency is an added benefit. Disadvantages include RF noise emission (both radiated and conducted), increased complexity, and susceptibility to voltage spikes and surges.

These things can be made quite well, with low levels of RF emission. But well-made usually equals high-priced. An el-cheapo device with an AC output fed through zip cord sounds like a sure-fire way to destroy radio reception for a fair distance around. Does the power supply have an FCC part 15 label or something similar on it?