When extremely low ripple is required, or when the voltage supplied to the load must remain constant under conditions of large fluctuations of current and line voltage, a closed-loop amplifier is used to regulate the power supply. There are two main categories of electronic regulators. They are:

Electronic power supply regulators are broadly divided into two main categories: linear regulators and switching regulators. Linear regulators operate by dropping excess voltage across a series element (like a transistor) which dissipates the extra energy as heat, providing extremely clean and low-ripple output. Switching regulators rapidly switch the power on and off, storing energy in inductors or capacitors. This makes them highly efficient, though they can introduce high-frequency noise. Distractors like 'stiff' refer to a power supply's ability to maintain a constant voltage under varying loads, not a category of regulator design, while 'non-linear' is simply a false contrast in this context.