Power supplies which convert AC system voltage to direct DC voltage, typically 230 VAC to 12 VDC, 24 VDC or 48 VDC.
Depending on the nature of the load, different demands are made on filtration of the direct voltage or content of AC components (residual ripple). "Advanced" electronics such as burglar alarms and audio equipment typically make greater demands on the power supply than DC motors and contactor coils.