When you hear about a switching power supply ... you want to make and break a DC circuit in that way. Simple. With a little filtering, you get some sort of AC output, and AC is manageable with ...

The first is that the power supply uses less electricity than a linear power supply. The second is that the switching ... diagram of a PC power supply. Red lines are AC, green lines are DC.

A DC power supply circuit operating in forced continuous conduction mode (FCCM) only produces audible noise within the speech-sensitive audio frequency range (e.g. GSM pulses or other periodic loads).