Power supplies lack glamour, so nearly everyone takes them for granted. That's a big mistake, because the power supply performs two critical functions: it provides regulated power to every system component, and it cools the computer. Many people who complain that Windows crashes frequently understandably blame Microsoft. But, without apologizing for Microsoft, the truth is that many such crashes are caused by low-quality or overloaded power supplies.
If you want a reliable, crash-proof system, use a high-quality power supply. In fact, we have found that using a high-quality power supply allows even marginal motherboards, processors, and memory to operate with reasonable stability, whereas using a cheap power supply makes even top-notch components unstable.
The sad truth is that it is almost impossible to buy a computer with a top-notch power supply. Computer makers count pennies, literally. Good power supplies don't win marketing brownie points, so few manufacturers are willing to spend $30 to $75 extra for a better power supply. For their premium lines, first- and second-tier manufacturers generally use what we call midrange power supplies, better than the Pacific Rim junk used by some garage shops and low-end assemblers, but not nearly as good as what you can get on the aftermarket. For their mass-market lines like those sold at Circuit City, Best Buy, and Target even name-brand manufacturers may compromise on the power supply to meet a price point, using what we consider marginal power supplies both in terms of output and construction quality.
The following sections detail what you need to understand to choose a good power supply.