Linear regulated power supplies excel by their highly constant output voltage, low ripple and fast regulation, even under high line and load transients. Good power supplies feature a ripple of less than 1 mVrms which is mostly neglegible. Further they are free from EMI emission in contrast to SMPS.

A conventional mains transformer isolates the line from the secondary which is rectified and supplies an unregulated voltage to a series pass transistor. Capacitors at the input and output of the regulator serve as buffers and decrease the ripple. A high precision reference voltage is fed to one input of an amplifier, the second input is connected mostly to a fraction of the output voltage, the output of this amplifier controls the series pass transistor. This analog amplifier is generally quite fast and is able to keep the output voltage within tight limits.