a regulated power supply

A regulated power supply adds a brain to the raw supply: a feedback loop that watches its own output and constantly adjusts to hold the voltage steady, no matter how the mains drifts or how much current the load demands. If the unregulated supply is a rain barrel, the regulated one is a water tank with a float valve that keeps the level dead constant whether it is raining or you are filling the bath.

Inside, the regulator compares its output to a fixed voltage reference (a stable yardstick) and drives a control element to correct any difference — exactly the thermostat idea of negative feedback. A linear regulator does this by varying a series transistor like an automatic valve, burning the excess as heat; a switching regulator does it by chopping the input on and off and storing energy in an inductor, which is far more efficient. Either way, the result is a rail that holds, say, 5.00 V across a wide range of input voltage and load current, with the ripple and drift hammered down by the loop gain.

Why it matters: almost every sensitive circuit needs a regulated rail. Digital logic latches up or resets if its supply sags; op-amps and ADCs measure against their supply or reference, so a wandering rail corrupts every reading; precision analog needs millivolt stability. Two honest numbers describe how good a regulator is: line regulation (how little the output moves when the input changes) and load regulation (how little it moves when the load changes). Both should be tiny — often a fraction of a percent.