What is the purpose of the rectifier in a linear power supply?

A rectifier is a circuit built using diodes, which are electronic components that only allow electrical current to flow in one direction. When alternating current (AC) from the transformer enters the rectifier, the diodes force the current to become pulsating direct current (DC). This conversion from AC to DC is the sole purpose of the rectifier in a power supply. Without it, the alternating current would continuously reverse direction, which would prevent sensitive DC-powered radio equipment from functioning. Do not confuse the rectifier with other power supply stages. Once the rectifier creates the pulsating DC, it is the filter's job to smooth those pulses out, and the regulator's job to hold the final voltage constant under a heavy load.