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Power supplies are charged with supplying the right amount of juice to each and every component sitting inside your PC. If you want to know how to pick the right one for your rig, read on as Windows explains all...

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By  Jason Saundalkar Published  November 15, 2007

Each and every component sitting inside your PC's chassis requires a certain amount of power to function. This is supplied by a device known, unsurprisingly, as a power supply unit (PSU), which sits inside the case (usually above the motherboard, towards the roof of the chassis).

PSUs are designed to convert the mains voltage - from your wall socket - of 110-or 240-Volts AC (Alternating Current) to several lower-voltage DC (Direct Currents) outputs that the machine's internal components use. 110-120 line voltages are used in North America and Japan, whereas the 220-240 line voltages are used across Asia, Australia and Europe, including here in the Middle East.

Whilst some modern PSUs are capable of working with both 110- and 240-voltages, there are some that are only compatible with one or the other. So, if you are building a PC to take overseas with you, pick a model that supports both ranges (as if you connect a PSU that is only 110-volts compatible into a mains supplying 240-volts, the supply will literally go up in flames! On the flipside, if you hook up a supply designed to work with 240-volts to a 110-volt mains, the machine simply won't power up.

The ratings game

Each and every PSU has a particular rating - such as 300- or 450-watts - which refers to the wattage the manufacturer claims its model can deliver to your PC's components. Unfortunately, there is no international standard in place that governs exactly which figure a manufacturer can publish as their PSU's wattage.

As a result some firms use figures as they please, thus comparing one PSU to another is not as straightforward as comparing their wattages. For example, one firm might quote the model's peak wattage rating whereas another more reputable manufacturer may use the continuous wattage rating. (The latter is a far more accurate figure because this refers to the constant or continual wattage the PSU is capable of delivering. The former relates to the absolute peak wattage that the supply can deliver; meaning its constant wattage delivery would likely be lower by 100- or even 200-watts.)

In the real world then, if connecting, say two of these 500-watt rated PSUs to a machine - in turn - that actually requires 500-watts of power for its components, the model with the 500-watt peak rating would likely fail. This is simply because its continuous wattage rating may actually be only 350-watts.

Depending on your PC's exact specifications, you'll need to buy a capable power supply so that all your components get the power they need to function properly. You can't for instance buy a model rated at 350-watts and expect it to power a machine that actually requires 500-watts. While the power supply may initially be able to do this, it is running overloaded and will eventually fail or explode, which could also damage your components. Although some high quality power supplies may survive for longer periods of time when they are over burdened, the machine they're powering will likely crash or freeze frequently.

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