Adopting either 20 or 24 pin connection to the motherboard, a single device delivering both 5 volt and 12 volt supplies to the entire system depending on the architecture of the device.
The power supply also connects directly to the devices housed within the case.
The power supply unit converts Alternating Current (AC) to a more usable Direct Current (DC) which is low voltage for use with components such as the motherboard. Some power supplies have a switch to change between 230 V and 115 V. Other models have automatic sensors that switch input voltage automatically, or are able to accept any voltage between those limits.
Power supplies for laptops are battery based therefore they can be re-charged and function without a direct connection to a plug socket. Servers usually contain 2 power supply units. This is due to their need to businesses that if one power supply fails then the backup PSU kicks in and the server is still powered.
In a personal computer (PC), the power supply is the metal box usually found in a corner of the case, it also tends to have a large warning label on it to remind you of the residual current present. The power supply is visible from the back of many systems because it contains the power-cord receptacle and the cooling fan.
The power supply distributes a range of watts to individual parts of the PC. Such as 12 Watts is used to power the hard drive and lower wattages are distributed to other components.