Any electrical device, including a computer, needs power in order to operate properly and the device responsible for supplying that power is, creatively enough, called the power supply. What the power supply actually does is converting the alternating voltage (AC), supplied by the power system, into continuous voltage (DC). In other words, the power supply converts conventional 110V or 220V alternating voltage into continuous voltage required by the PC electrical components which are +3.3V, +5V, +12V and -12V. AC voltage may vary throughout the world, but in order to simplify the matter, we will use 110V to include 110V, 115V and 127V, whereas, for voltages of 220V, 230V and 240V, we will use the 220V label. Australia’s power grid, for example, uses 230V, while Japan is the only country in the world outside this range and its residential voltage is 100V.
You can find two basic designs of power supplies Australia wide: linear and switching-mode.