All power supplies provide electrical energy to do work, but how the feat has been accomplished over the centuries has varied considerably. The first power supplier was the Leyden jar. Invented in 1745, it could store sizeable electric charges created by electrostatic devices, such as Alessandro Volta's electrophorus. The charge could be drawn from the jar and put to work. In 1800, Volta created the first battery, the "Voltaic pile." This reliable source of power produced electricity by means of a chemical reaction.

The first mechanical electrical generator was invented by Michael Faraday in 1831. Joseph Henry and Faraday had independently discovered that a moving magnetic field could create the flow of electricity in a conductor. Faraday used this process of electrical induction to create an alternating current power supply. Soon after, Hippolyte Pixii built a hand-driven generator that produced alternating current (AC), and added a commutator to convert...