Just for fun, I tried turning a CP2102 USB UART adapter into a PDM DAC, using the raw output of the serial bitstream. It sounds "not good", but honestly not that bad either. Here's a sample from it: https://retr0.id/media/5c4c16ac-bc6d-4bf0-9159-73bbe4fcfb02/...
The only external components were a simple passive RC filter.