Power supplies, otherwise known as electric power converters, are electronic devices used to supply electricity to an electrical load. They don’t store energy, but instead receive electrical energy from an outside source such as the electricity grid, a generator, an alternator, or energy storage devices like batteries or fuel cells.
Power supplies perform a very important function: they reduce the power supplied to a voltage level that is suitable for powering the load. The component that performs this function is called a Power Supply Unit (PSU). PSUs can also be used for converting AC input power to DC power (with a DC PSU). Finally, regulated PSUs ensure that power supplied to the load is constant, even if the AC supply voltage changes. This is important for the proper functioning and longevity of electrical load components.