Choosing the Right Power Supply

Written By: Keith Park

The power supply is the least respected and most overlooked component in your PC. No one ever talks about how big their power supply is, all you ever hear is how fast their CPU runs, or how much memory they have, or how many MP3′s they can fit on their hard drive. The only time anyone ever talks about the power supply is when they got one really cheap or it was included free with their case.

Did you know that when manufacturers build their low cost systems one of the components they downgrade is the power supply?

You may think, so what? Well, here is an analogy.

You buy a new “low-cost” PC and as time passes you add components to it. You install a second hard drive, you get a bigger video card with a built in fan and you add a USB PCI card for extra ports. Then one day your PC starts rebooting on itself for no apparent reason. You can’t figure out what is going on. You install all the Windows updates, run a virus scan, check for Spyware — nothing there! What’s up? Little did you know that by buying that “low-cost” PC you also got yourself a very cheap quality, 200 watt power supply. All the new components you have added over time —- the power supply can’t pump out enough power to keep up and even when it can supply enough juice, the quality of the power signal is unstable.

If you are going to spend the big bucks on all the other components in your PC, why skimp out on the power supply? A cheap no name power supply can cause system instability as well as damage other components in your PC that you have paid so much money for.

The Power Formula

In order to get the right power supply for your situation you need to take into account everything that is going into your PC as well as plan for any future additions or upgrades you may perform.

Write down every component going into your system and the watts required for each (Most devices will have the power information listed on the unit itself, the documentation that came with the device or the website of the manufacturer), now add them up, this will give you the maximum watts that your system could potentially use.

Another piece of the puzzle that must be considered is how many amps are being drawn by the components on each of the 3 main outputs (rails) of the power supply, +3.3, +5, and +12. These specs are a little harder to find. Some manufacturers will list this information on the device or documentation but most do not want to bore consumers with such detail. If your component doesn’t have this information, you can find an estimate by doing a search on the Internet for a particular component. I did the following search using Google — how many amps does a floppy drive draw from the power supply — and got back the result of, 1.0 amp of +5v power.

Now that you have all the numbers added up you need to find power supply that meets your needs. Both numbers you have are equally important, you may find a 400W power supply that will run everything you have but it will lack the power to meet your needs when it comes to the 3 main outputs.

One note of interest, as with most things in life, what it says on the box isn’t always what you get when you open it. Most power supplies fall short of the wattage spec listed on the box so this must be taken into consideration when making your final decision.

Other Considerations

Warranty – Make sure you get a warranty with your power supply and consider the length of the warranty. If you plan on keeping your PC for 3 – 5 years then getting a power supply with only a 90 day or 1 year warranty maybe isn’t the best idea.

Cables/Connections – Check the length and number of cables on the power supply. If you don’t have enough connections or the cables are too short to reach all your drives it can be really frustrating. Also, if you plan on connecting a SATA drive then you need a power supply that has the proper connection for it.


The power supply you need to buy completely depends on YOU!

There is no use buying a 500W top of the line power supply if you will never use 500W — stick to what you need. As long as you do the math you should be safe.

Buy from the major manufacturers, Enermax, Antec, etc. They offer quality products with good warranties.

Finally, check out the Internet and see what others are saying about power supplies, which ones are good, which ones are bad. Reading reviews and others opinions can be a source of good information.

About the Author

Keith Park has been in the IT industry for the last 7 years and is the author of the website TechCorner PC Resource Zone. Go there for more articles and resources.

Additional resources @ http://mgrcentral.com/computers/default.aspx?studentid=1575219

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