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PC Power Supply Buyer's Guide

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Power supply unit
public domain/Wikimedia Commons

Power supply units (PSUs) are often overlooked when building a desktop computer system. A poor quality power supply can greatly reduce the life span of a good system or cause instability. A high quality one can also help reduce the noise or heat generated within a computer system. Whether you are buying one for a new computer or replacing a old unit, here are some tips for purchasing a desktop PC power supply.

Avoid Power Supplies Under $30

Most power supplies that are priced below $30 generally do not meet the power requirements of the latest processors. To make matters worse, the components used in them are of inferior quality and more likely to fail over time. While they may power the computer system, inconsistencies in the power to the components will tend to cause instability and damage to the computer over time.

     

    ATX12V Compliant

    Developments in processors, the PCI Express bus and graphics cards have all increased the amount of power required to operate them. To help provide this extra power, the ATX12V standard was developed. The problem is that it has been revised over time with various different power supply connectors to meet the necessary specifications. Make sure that it comes with the proper main power leads that you need for your motherboard.

     

    Knowing the Wattage Ratings

    Wattage ratings on power supplies can be deceptive as this is the total combined wattage of all the voltage lines and generally under peak rather than sustained loads. With the increased demands by components, the total required output particularly for the +12V line has become increasingly important especially for those that are using dedicated graphics cards. Ideally a power supply should have at least 18A on the +12V line(s). The actual load you need will vary depending upon your components.

     

    Low or No Noise

    Power supplies generate a lot of noise from fans used to keep them from overheating. If you don't want a lot of noise, there are a number of options available. The best choice is for a unit that either uses larger fans that move more air through the unit at slower speeds or to get one with temperature controlled fans. Another option is fanless or silent power supplies that generate no noise but these do have their own drawbacks.

     

    MTBF: Mean Time Between Failures

    MTBF (mean time between failure) is the rating given by a manufacturer for the typical amount of usage a unit will have before a possible failure. Roughly 50% of units fail before this and 50% live longer. The higher the MTBF rating, the better the quality of the power supply. Avoid units with ratings of below 20,000 hours as this only equates out to roughly 2.25 years of continuous usage. Unfortunately, many power supplies will not list this or they bury it under their technical specifications.

       

      Power Efficiency

      Power supplies convert voltages from wall outlets to lower levels used by the PC. During this conversion, some power is lost as heat. The efficiency level of the PC determines how much extra power must be put into the power supply to run the PC. By getting a more efficient power supply, you end up saving money through the use of less overall electricity. Look for a unit that has the 80Plus logo showing that it has passed certification. Just be warned that some of the highest efficiency power supplies may cost so much more that the power savings does not match their increased cost.

       

      Having the Right Type And Number of Connectors

      There are a variety of different power connectors that come off a power supply. Some of the different connectors include 20/24-pin power, 4-pin ATX12V, 4-pin Molex, floppy, SATA, 6-pin PCI-Express graphics and 8-pin PCI-Express graphics. Take stock of what power connectors your PC components require to ensure you get a power supply with the appropriate connectors. Even if it might lack some connectors off the power supply, check what cable adapters the power supply may include to mitigate the problem.

         

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