Which of the following is not considered a power supply?

In the context of electrical engineering and power distribution, a capacitor is not considered a primary power supply. Instead, it serves a different role in electrical circuits. Capacitors are passive electrical components that store and release electrical energy in a circuit. They help in filtering, smoothing, and coupling applications, rather than supplying power directly to a load.

Transformers, batteries, and generators are classified as power supplies because they convert or generate electrical energy for use in circuits. A transformer steps voltage up or down in AC systems, a battery stores chemical energy and converts it into electrical energy, and a generator converts mechanical energy into electrical energy. These devices actively provide power to electrical systems, which distinguishes them from capacitors, whose main function is to manage and store electric charge rather than generate or supply it.