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So the Power Supply supplies power. Why should I care?

Updated on March 20, 2011

Every computer has a Power Supply Unit (PSU) and most users rarely give it a second thought. You plug in the cord to that socket in the back, push the button and your computer runs. So what?

It turns out that the PSU is an incredibly important computer component and the majority of PCs out there have insufficient, inadequate, or downright faulty PSUs.

Yeah. You read correctly. If you're running any Pentium IV, Core 2, Athlon X2 or Phenom processor the chances are that your PSU is not providing the quantity and quality of electric current that your system requires.

The PSU converts 110 to 240 volt AC power from your wall outlet into the specific 3.3 to 12 volt DC electricity that your motherboard requires. If your motherboard had access to juice straight from the mains it would explode in seconds. The inside of the PSU metal box contains voltages that can kill you so open it up only if you are suicidal.

Eeny meeny miny moe... catch a PSU by the toe...
Eeny meeny miny moe... catch a PSU by the toe...

Most modern PCs only require the +3.3, +5 and +12 volt feeds, the first two for most of the circuitry and the last one for the mechanical motors in the drives, fans, etc. However, almost all PSUs also provide -5 and -12 volt power for prehistoric features like floppy drives and serial ports that have gone the way of the Dodo bird, big chrome tailfins and the McRib Sandwich.

From the back of the PSU runs a thick sheaf of multicolored wires. These are color coded according to the current they carry.

Ground: Black

Power Supply On Indicator: Green

+3.3 volt: Orange

+5 volt: Red

+12 volt: Yellow

Useless -5 volt: White

Even More Useless -12 volt: Blue

These wires have a whole bunch of different connectors on them, some to plug right into the appropriate socket on the motherboard, older IDE disk drives, newer SATA drives, etc. The rule is, if it fits (without hammering it in) then it's the right connector.

Each power supply has a wattage rating clearly noted on the side of the box. This number is the total capability of the power supply's rails all added up together. The necessary 5 volt, 12 volt, and 3.3 volt, the useless -12 volt and -5 volt (as well as the 5VSB) capability are all lumped in together to come up with the total wattage rating. That number is well nigh meaningless and is pretty well best disregarded.

A critical factor for a power supply is whether it can provide smooth, even current to your entire system under maximum load. Given the fact that Nvidia's newest top of the line video card will suck almost 240 watts out of the PSU, and it's best combined with a hot processor that can call for another 135 watts, you will see that even the best quality 300 watt power supply will only have a few watts left to run the rest of the PC. That is not nearly enough and you will require plenty of overhead. A good rule of thumb is to add up the wattage requirements of your total system at max and add 50% to find the wattage rating you need for a power supply. I say to heck with that and double it. Better safe than sorry!

Where most people run into trouble with PSUs is that they read the specifications on the side of the box and assume that "wow... since it is rated at 420 watts, that's more than enough!" What they don't understand is that the wattage rating they are reading is illusory at best. There are some quality PSUs rated at 300 watts that will adequately supply power to a state of the art personal computer system where some cheap Chinese 650 watt PSUs will fail and end up corrupting your data, frying your computer or even worse.

There are so many variables to take into consideration when determining which PSU will provide the optimal current to your PC system: amperage distribution across the rails, temperature, de-rating curve, resistance, independent voltage regulation and crossloading... are your eyes crossloading yet? They should be! To fully understand PSUs you should get a Ph.D. from PS University!

By far the best way for the average computer user to determine which PSU to plunk into his build is by brand name and price. There are a lot of knowledgeable PSU buyers out there and the current sales price at major etailers is a pretty good indication of the quality of each unit. If you see that the general going price of a Whatasparky 550W is $40 more than the Zapyomama 550W PSU, then you can be pretty well certain that the former is the quality unit. There are some PSUs that sell for under $25 and that includes the complete mid tower case. Need I spell out what they're good for? Connect this junk to your quality computer components and watch them all die a miserable death.

All manufacturers have variances in quality and performance from one model to the next, therefore it is quite difficult to discern just by brand name if your PSU is top quality or not. The situation is confused even further by the fact that several manufacturers offer exactly the same PSUs under their own brands at all sorts of price points and even varying wattage ratings! Here is a very general and extremely approximate guide to the pecking order of PSU manufacturers:

These are arguably the best in the industry, the true indisputable gold standard, and you will likely pay for the quality but it will be worth it in reliability and stability.

  • Emacs

  • Enermax

  • PCP&C

  • Seasonic

  • Silverstone

  • Zippy

These are really great, top notch, high quality manufacturers.

  • AbleCom

  • Akasa

  • Antec

  • CoolMax

  • Cooltek

  • Corsair

  • Enhance

  • Fortron

  • Hiper

  • iStarUSA

  • Mushkin

  • OCZ

  • SevenTeam

  • Supermicro

  • Tagan

  • Thermaltake

  • Ultra

  • Xclio

  • Zalman

Excellent mid-range PSU manufacturers for systems without a lot of power hogging expansion cards or hot/overclocked processors.

  • Acbel

  • AMS

  • Athena

  • Be Quiet

  • Channel Well

  • Epower

  • Sparkle

  • Spire

  • Sunbeam

You're generally better off to steer clear these brands unless you are putting together a really budget-conscious build.

  • Aerocool

  • Asus Atlas

  • BFG

  • Cooler Master

  • Delta

  • E-Power

  • Enlight

  • Futurepower

  • Hipro

  • Lite-On

  • Masscool

  • MGE

  • NorthQ

  • Scythe

  • Sintek

  • Superflower

  • TTGI

Avoid! Avoid! Danger, Will Robinson!

  • A-Top Technology

  • Apex

  • Allied


  • Atrix

  • Broadway

  • Deer

  • Diablotek

  • Dynapower

  • Eagletech

  • Foxconn

  • I-Star

  • In Win

  • JPAC

  • Just PX

  • Kingwin

  • Liberty

  • Linkworld

  • Logisys

  • MGE

  • MSI

  • NMediaPC

  • Norwood

  • CompUSA

  • NZXT

  • Powmax

  • Q-Tec

  • Raidmax

  • Rosewill

  • SFC

  • Shuttle

  • Skyhawk

  • Star Micro

  • Startech

  • Supercase

  • Topower

  • Wintech

  • Xion

  • Youngyear

  • Zebronics

and any other name that is not on this list!

Choosing the proper PSU to plunk into your PC is one of the most important selections you will make for the long term reliability, stability and performance of your system. You are well advised to do your homework and don't scrimp on this extremely critical component!


Check out hundreds of Hal's PC Technology articles in these categories:


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