Recently, I got a Fuji 48V, 40A PSU (telecom "rectifier") for basically scrap value (about $15). As usual, I did a teardown to learn about what's inside. It certainly looks impressive as you might expect, with a resonant full bridge design. To power it on, connect the short pin in the output connector with the two pins directly below it.
As for uses, the most obvious would be a high power audio amplifier. With about 2kW continuous, any amplifier that can even begin to challenge that PSU would likely be overkill for even a high end home theater. Another good use could be a fast charger for a DIY hybrid bicycle or electric riding mower.