What is a Power Supply?

A power supply is an electrical device that converts the electric current that comes in from a power source, such as the power mains, to the voltage and current values necessary for powering a load, such as a motor or electronic device.

The objective of a power supply is to power the load with the proper voltage and current. The current must be supplied in a controlled manner — and with an accurate voltage — to a wide range of loads, sometimes simultaneously, all without letting changes in the input voltage or in other connected devices affect the output.

A power supply can be external, often seen in devices such as laptops and phone chargers, or internal, such as in larger devices such as desktop computers.

A power supply can either be regulated or unregulated. In a regulated power supply, the changes in the input voltage do not affect the output. On the other hand, in an unregulated power supply, the output depends on any changes in the input.

The one thing all power supplies have in common is that they take electric power from the source at the input, transform it in some way, and deliver it to the load at the output.

The power at the input and output can be either alternating current (AC) or direct current (DC):

  • Direct current (DC) occurs when the current flows in one constant direction. It usually comes from batteries, solar cells, or from AC/DC converters. DC is the preferred type of power for electronic devices.
  • Alternating current (AC) occurs when the electric current periodically inverts its direction. AC is the method used to deliver electricity through power transmission lines to homes and businesses

Therefore, if AC is the type of power delivered to your house and DC is the type of power you need to charge your phone, you are going to need an AC/DC power supply in order to convert the AC voltage coming in from the power grid to the DC voltage needed to charge your mobile phone’s battery.