The power supply's main function is simple: take the power input to it from the power system of your home or office, and turn it into a form that the PC can use.

The PC power supply must provide several different voltages, at different strengths, and must also manage some additional signals that the motherboard uses.

Absolutely vital, Without it, a computer is just an inert box full of plastic and metal.

Converts the alternating current (AC) line from your home to the direct current (DC) needed by the PC.

Psu is the metal box usually found in a corner of the case.

Psu is visible from the back of many systems because it contains the power-cord receptacle and the cooling fan.

The electricity you get from your utility company is in the form of alternating current (AC), while the electricity your PC requires is direct current (DC).

Therefore, the primary function of your power supply is to convert your wall AC power into a DC form that your PC can use.

In fact, the supply normally provides several different voltage levels, to meet the demands of different components in the machine.

Psu, often referred to as "switching power supplies", use switcher technology to convert the AC input to lower DC voltages.

The typical voltages supplied are:

3.3 volts

5 volts

12 volts

The 3.3- and 5-volts are typically used by digital circuits, while the 12-volt is used to run motors in disk drive and fans.

The main specification of a power supply is in watts

A watt is the product of the voltage in volts and the current in amperes or amps.

Prior to 1980 or so, power supplies tended to be heavy and bulky. They used large, transformers and huge capacitors (some as large as soda cans) to convertline voltage at 120 volts and 60 hertz into 5 volts and 12 volts DC.

Power supplies used today are much smaller they convert the 60-Hertz (Hz, or cycles per second) current to a much higher frequency, meaning more cycles per second reducing the variances in voltage for the sensitive electronic components in the computer.

Over time, there have been at least six different standard power supplies for personal computers.

The industry has settled on using ATX based power supplies for now.

PC power-supply cables use standardized, keyed connectors that make it difficult to connect the wrong ones.

APM offers a set of 5 different states that your system can be in. (Developed by Microsoft and Intel.)

The 5 different states

Always on

Sleep

Snooze

Hibernation

Standby

A 400-watt psu will not necessarily use more power than a 250-watts.

A larger supply may be needed if you use every available slot on the motherboard or every available drive bay in the personal computer case.

It is not a good idea to have a 250-watt supply if you have 250 watts total in devices, since the supply should not beloaded to 100% of its capacity.

AGP = 30 W

3 X PCI = 15 W

Floppy Disk Drive = 5 W

CD-ROM X50 = 25 W

RAM = 10 W (128)

Hard-Drive = 11 W

Motherboard = 30 W

550 Pentium III = 30 W

Total = 156 W

 

PC power supply is probably the most failure-prone item.

Typically, a stalled cooling fan is a predictor of a power supply failure due to subsequent overheated.

Typical failure of a PC power supply is often noticed as a burning smell just before the computer shuts down.

Failure symptoms include random rebooting or failure in Windows for no apparent reason.

Revolutions per minute (RPM) of the power supply fan via BIOS.

New designs offer fan control so that the fan only runs the speed needed.

Some servers have two psu’s, one is your primary and one is your secondary .The secondary is your backup psu.

The backup supply immediately takes over in the event of a failure.