In a regulated power supply, components that conduct alternating current at the input before the transformer and direct current before the output are:

Fuses are basic safety devices designed to protect electronic circuits from overcurrent conditions. Because a fuse is essentially a calibrated piece of wire designed to melt at a specific current threshold, it acts as a simple conductor that works equally well with alternating current (AC) and direct current (DC). In a typical power supply, a main fuse is placed on the AC primary side (before the transformer) to protect against catastrophic short circuits. Another fuse is often placed on the DC output side to protect the power supply components from a faulty load. Capacitors block DC, chokes oppose changes in AC, and diodes restrict current to a single direction. Only the fuse acts as a transparent conductor for both AC at the input and DC at the output.