This document discusses power supplies and their components. It begins by explaining the differences between alternating current (AC) and direct current (DC), and how each is produced. It then discusses what a power supply is and its main components, including transformers, rectifiers, filters, and voltage regulators. The document outlines the basic stages in a power supply and different types of rectifier circuits. It concludes by describing some common internal and external parts of a power supply like capacitors, diodes, switches, and connectors.