You will always find a metal box inside of a personal computer (PC). This metal box is often visible on the back of the computer, since it contains the power-cord receptacle and the fan that cools the computer down since the electicityy heats everything up. Power supplies are often reffered to "switching power supplies", since they switch the higher AC current to the lower DC one because as explained above, the components in a computer cannot function if the electricity voltage is too high, they will be damaged. So the power supply makes this avoidable.
The typical voltages supplied are:
- 3.3 volts
- 5 volts
- 12 volts
The first two are more typically used by digital circuits, while the 12-volt is used to run motors in disk drives and fans. The main power supply is watts. In the first PCs you had to manually switch a red toggle switch, which was probably very tiring, and all you now have to do it push a button on the computer to shut it off or turn it on, or then just shut the computer down via the menu bar. The button you push sends a 5 volt signal to the power supply, which tells it to turn on. Awesome! It then sends power to the motherboard, to the optical drive and the monitor just to name a few.Sources: http://computer.howstuffworks.com, http://www.hardwaresecrets.com/article/181 and http://www.hardwaresecrets.com/article/Everything-You-Need-to-Know-About-Power-Supplies/181