What Is a Power Supply?
The power supply (PSU) is can be likened to the heart of a computer. It provides the energy (electric) for all the electric powered computer components, such as the processor, motherboard, memory modules, graphics cards, as well as storage and optical drives. The power supply is connected to the house / office wall socket and converts that alternating current (AC current) into a specified voltage direct current (DC current) which is used by the computer components.

It is unfortunate that a lot of users do not pay significant attention to the computer PSU, however since it is the heart of the PC, there should be no compromise on it. A cheap power supply can lead to fried computer components due to improper voltage stabilization and unfiltered power. A high quality power supply on the other hand clean power to all components and allows for maximum uptime. A defective or inadequate power supply can result in random system resets/freezes.

Maximum Power
Power supplies are generally classified by their output wattage, which is quoted according to the “Maximum Power” output. Common power supplies range from 350-1200 Watts.

It is important to note that the maximum power alone cannot be used to choose what supply you would need to to drive your computer. Power supplies have voltage rails, which you need to pay attention to. The most important voltage rail is the +12V rail(s), since it feeds the processor and PCIe graphics cards, which are generally the two most power consuming parts of any computer. The voltage rail should have an output of at-least 18A (amps) on the +12V rail(s) for an everyday use computer; above 24A for a gaming PC with a dedicated graphics card; at-least 34A when for high end SLI/CrossFire systems.