Electrical Power Supply - Plug-in Power Supplies

The electrical energy supply for homes and businesses provided through the commercial power lines is delivered by an alternating current (AC). Electronic equipment, however, almost always requires direct-current power (DC). Power supplies usually change AC to DC by a process called rectification. Semiconductor diodes that pass current in only one direction are used to block the power line's current when its polarity reverses. Capacitors store energy for use when the diodes are not conducting, providing relatively constant voltage direct current as needed.