What does power supply do?

Answer 1

A power supply does not create power or energy. This would be in violation of the Law of Conservation of Energy.

Rather, a power supply changes the form of an available source of power or electrical energy into a form that is acceptable for use by electrical or electronic equipment.

The input form is electrical energy defined by voltage or current or power, with a given impedance level, and frequency. The output form from the power supply is a different voltage or current or power, with a different impedance level, and possible a different frequency. Another possible is for the input and output to be of the same form but electrically isolated from each other for safety and performance concerns.