A power supply is a radio with a boring station.
Traditionally, crystal radios only use one diode for half-wave rectification. That probably dates back to when the diode was the most expensive part of the radio.
I have a parts drawer with at least a dozen Germanium diodes*, so why not use 4 diodes for twice the signal output? (I have seen circuits with two diodes and a coil center tap. That’s full-wave rectification, but half the voltage.)
* they produce a warmer sound.
