Computer Power Supply Unit (SMPS)

SMPS - Switch Mode Power Supply - is the technical term for what we generally know as the computer power supply unit. It is basically a box-like device used for the supply of power to your computer unit. So what does it do? In very simple terms, it converts the AC (Alternating Current) power supply from the general electrical sockets available at your home to DC (Direct Current), basically the type of current you get from a battery. The "Switch" term in the SMPS comes from the fact that the computer power supply unit converts AC to DC using switcher technology. We now use the ATX supply power units for the computers as the industry has settled on a standardized case and motherboard (ATX).

Typically, three voltages (12V, 3.3V and 5V) are supplied by the power supply unit.

If you are selecting a computer power supply unit, how do you go about doing that?

1. The first thing of course is to know what power requirements you are looking at. You can check the power requirements of the various devices of your computer and add them up, or you can just ask the vendor for the same. Once you have the total wattage, (that will be the unit of power), you can go for a slightly higher rated SMPS.
Now why you want to do that is because, at a later point of time, if you want to upgrade your computer, like a new DVD RAM drive, you may need a higher power supply.
One more thing to remember is to check the actual wattage against what the label on the power supply unit indicates.

2. It is always a good idea to go for a branded power supply unit. But that might not help if price is an important criteria.
The SMPS supplies power to all the components of the computer, like the motherboard (24/20 pins), hard drives and CD ROMS etc (IDE 4-pin), floppy drives (Floppy 4-pin), etc.
What happens is that, once the computer is powered on, there is a surge of current and as a result, it gets heated up. The fan, in such a condition is crucial, other wise, high temperatures might result. You should have at least one 80mm fan. It is even better if there are two fans instead of one.
(One such problem is the continuous restart of your computer as the temperature rise due to a faulty power supply causes the computer to shut down without giving any error message, and in some cases, not even the BIOS screen.)

If you have a branded SMPS, you can rest assured that there is not much chance of such an event occurring.

3. Number of connectors and the efficiency rating – These two factors are at par with the other factors while considering the computer power supply unit. The efficiency rating, is important as it is directly related to the heat output and subsequent temperature rise. Higher efficiency rating ensures that the SMPS causes a lesser rise in temperature.
The number of connectors is important as it determines how many devices you can use with your computer.

4. Lastly, the noise level – Apart from the CPU fan, the SMPS fan also determines the amount of noise generated – Except from a fine whirring sound, which is basically indistinguishable, you should not have any other sound coming from the SMPS.