Every power amplifier requires a power supply and a power output stage.

Class "D" amplifiers and switched mode power supplies have Pulse Width Modulation (PWM)  in common..

The power supply and power output stage can be combined, and this concept is the basis of design and patent of the  "Direct Audio From a Power Supply" (DAFPS) amplifier. US Patent No's.598,6498 and 6,392,476