Power Supply is the source of energy. Everything around you require energy.
Everything is made from the Energy. We, the humans are all part of energy as well.
All reactions require energy.
Power Supply Unit is the device that supply an electrical energy to an output load.
All power supplies have fuse in it as well as the main adapter to avoid the damage to motherboard and other components.
There are several types of power supplies. There are battery type, transformer AC type, and switched form power supply.
Switched mode power supply is the one that is used in the home PCs.
Other than fuse, it has many other features to avoid component damages such as crowbar circuit.
The amount of power used is measured in Wattage. Watt is the unit of electrical power.
The amount of energy required to carry the electrical current is called the Voltage.
The ''Voltage'' is the electrical potential difference( the electrical pressure). Volt, is the unit used to measure the amount of voltage.