The Truth About Power Supplies

ATX power supply

Most of them look alike although some of them come in souped up chassis meant to raise the blood pressure of the drowsy, sleep-deprived gamer. Others sport innovative cooling technologies, LED lights, high-performance silent fans and a glittering menu of bells and whistles. All the trimmings and extras aside, your power supply is the heart and soul of your PC system, though it certainly does not get nearly as much ink as the sexy components like the processor, hard drive and memory do.

Because your power supply is so important to the life of your system, when it's time to buy a power supply it is essential that you know the difference between a good power supply and one that is merely adequate. So, what should you look for in a power supply? That's the question our fearless editors seek to answer.

Not Just Any Power Supply Will Do

Most people tend to overlook the importance of their power supplies, but those days are quickly coming to an end. That's because your power supply is far more than just an unassuming gray or black box that you plug into an outlet before you crank up your computer. Now that gaming machines, extreme PCs and fast, powerful workstations crave increasing amounts of reliable power, you can no longer afford to overlook the role that your power supply has in keeping your PC happy, healthy and running to its full potential.

While folks will talk forever about gigabytes of storage, megahertz of speed, how well their video adapters perform, how their 64-bit AMD processors can run graphical circles around an Intel CPU, they spend precious little time considering the power supply. Yet, when you build a system for the lowest possible price, guess what component the manufacturer is most likely to cut corners on? You guessed it, the power supply. As a result, you might just get caught with your pants down when you buy a PC system.

If you are paying attention to the power supply, there is a decent chance you are concerned mostly with how many watts of power it is rated to generate, even though at press time there is little chance you will be able to verify those power ratings. Unfortunately, many do not take the time to consider whether the power the supply produces is clean and stable, whether it is noisy, or if it is prone to system-jeopardizing spikes and surges.

The Increasing Demands on Power Supplies

It seems that only the PC connoisseurs, those putting together or purchasing extreme PCs or top-flight gaming systems, consider the power supply to be the heart and soul of the system and who always seek the best power supplies they can afford. The power supply is important simply because it supplies electrical power to every other component in the system. Unfortunately, it's historically one of the components most likely to fail, especially because so many manufacturers cut corners on quality when adding power supplies to their systems.

It's sad to say that a power supply on the fritz can cause components to malfunction as well as damage them by delivering improper or erratic voltage. As you add more and more peripherals to your PC system - extra hard drives, CD drives - anything that you plug into your motherboard - you put increasing strain on your power supply. The more strain the power supply must bear the more likely it is that you will have problems with inconsistent levels of power.

When your system is deprived of a consistent stream of reliable power it will be prone to random hardware failures, bizarre errors that you may never have seen before (and which you certainly do not want to see), or even the untimely demise of your prized personal computer. Yet despite the increasing importance of power supplies they are far from being the sexiest products in the computer supply catalogue or website.

We have certainly provided an excellent remedy to this dire situation, by giving power supplies great prominence on our easy-to-navigate site and by offering numerous products to suit the needs of every PC user at the most reasonable prices in the industry. Nevertheless, while the sight or thought of a great computer system can cause a savvy adult to salivate, that same individual often neglects to pay sufficient attention to what power supply is needed to run a powerful PC system.

Get Familiar with Power Supply Lingo

When you buy a PC or replacement power supply you should familiarize yourself about the power supply itself. Learn everything you can about it. The average consumer, however, tends to be intimidated by the vocabulary and complex statistics found in the specs. Here are a few common terms that can help make sense out of the specs.

Mean Time Between Failures (MTBF) or Mean Time To Failure (MTTF).

This value represents the calculated average hour interval that the power supply is expected to perform before it fails. Although power supplies will have MTBF ratings of 100,000 hours or more, be aware that these figures were not discerned from actual real-time testing. Most manufacturers glean these totals based upon the comparative failure rates of the power supply's individual components.

Overvoltage Protection.

Overvoltage Protection prevents a signal from being received if the voltage exceeds a certain limit. This helps prevent an electrical device from being overloaded and destroyed. Make sure the power supply you purchase includes overvoltage protection.

Maximum Load Current.

Maximum load current is the greatest amount of current, expressed in amps, which can safely be delivered through a particular output. Maximum load current values are represented as individual amperages for each output voltage. With these figures, you can calculate not only the total amount of power the power supply can supply, but also how many devices using those various voltages it can support.

Minimum Load Current.

The converse to maximum load current, minimum load current is the smallest amount of current (in amps) that must be drawn from a particular output for that output to function. If the current drawn from an output falls below the minimum, the power supply could be damaged or automatically shut down.

Load Regulation.

When the current drawn from a particular output increases or decreases, the voltage changes slightly as well, usually increasing as the current rises. Load regulation is the percent change in output voltage as the load is changed from minimum to maximum, at constant line and constant temperature. The load change may be specified for other than no load to full load, such as 20% load to full load.


The ratio of power that goes into a supply as opposed to how much goes out if it. This value is expressed in percentile, with the most common being within the range of 65-85 percent in today's power supplies. Be sure to purchase a power supply that falls within this range - the higher, the better! However, although greater efficiency translates to less heat inside the computer, which is something you should always strive for, precision, stability, and durability are more important factors.

So How Much Power Do I Need?

Obviously, we do not expect everyone to have all the terms of art down pat when it comes to power supplies. As you check out our power supply web pages you will notice these products come in a number of wattage designations. How much power is necessary for the "average" PC system, if there is such a thing nowadays? Take a look at what you've had in the past. If you bought a standard power supply from one of the top computer manufacturers, chances are you purchased a 250 to 300W power supply of average quality. Now that is more than enough for your run-of-the-mill system consisting of a hard drive, an optical drive and a fair-to-middling graphics card. However, if you are going to add more peripherals you need to seriously consider upgrading your power supply.

For your reference, following is a chart that illustrates approximately how much wattage you will need to run various common components in a PC system:

ComponentWattage Required
Low-end CPU20-50
Midrange to high-end CPU40-100
RAM7 per 128MB
PCI add-in card5
Low to midrange graphics board  20-60
High-End graphics board60-100
IDE hard drive10-30
Optical drives10-25

The Advantages of a Higher End Power Supply

The More Watts the Merrier

When you purchase a better power supply you will markedly decrease the amount of noise your computer makes when it's on. The fan that cools your power supply has to be a heavy performer to achieve its appointed task. Therefore, it's one of the biggest, noisiest fans in your PC. And it's strategically located in front of the vents that lead to the outside of your computer case. So, it makes a noticeable noise, one that can become irritating over time. A new, more efficient, more powerful power supply will deliver more power, regulate it at a more even level and at a reduced noise level.

For you PC builders, be aware that some of the inexpensive cases often come with cut-rate power supplies that may not be up to the task of powering a high-end PC. Some of the more expensive models do not come with a power supply, which give you the opportunity to choose your own. If you've added a lot of new components to your PC, you may be overtaxing your existing power supply, so look at getting a bigger, better one.

Power supplies can cause problems - including random crashes or even component failure - if they are asked to produce more power than they are designed to generate. Reputable manufacturers will typically include a chart of acceptable components.

Finally, Make Sure Your New Power Supply is Compatible with Your Computer. Beware - you must make sure your power supply is compatible with your system before you plug it in. Some computers use a special plug that links the power supply to the motherboard. If you use the wrong plug you can wind up literally torching your computer!

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