Here is the start of what I would like to become a definitive guide to Power Supply information.
Please feel free to suggest links or reviews that I do not already have....
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P.S.U.---- Power Supply Unit
ATX ---- being the most common... used for standard size, current generation, desktop configurations...
There are now several versions of the standard ATX design that include dual and even quadruple +12V rails, as well as a new SLI certification...
Only a few manufacturers have TRUE separate rails, most have 2-4 rails all coming from the same place...
Basically the SLI certification means little, as they have really only certified the "paper" specs and not the units ACTUAL performance...
What matters most is Quality and true performance under typical conditions instead of ideal...
Micro-ATX ---- used in slim, micro, flex, and small form factor cases, commonly lower wattage due to the all-inclusive nature of smaller builds...
And the proprietary style PSU's --- specifically built for pre-built commercial names like Dell, Gateway, Compaq, and H.P....
B.T.X. ----- Intel has now introduced a new form factor to replace ATX's supposedly haphazard layout...
LINK...( this form factor has not caught on due to temperatures going down and Intel not pursuing the design)
An alternative to using an SLI certified PSU wich can cost a great deal... if you have a decent PSU that just isnt up to an SLI setup, you can add an SLI certified "add-on" unit instead...
Newegg.com - ePOWER EP-350 CD 350W EPS12V SLI Ready CrossFire Ready Modular Dedicated Graphic Card and CPU Power Supply - Power Supplies Newegg.com - FSP Group Booster X5 450W Independent/Supplementary SLI Certified CrossFire Ready Modular Active PFC Dedicated Multi.GPU Power - Power Supplies Newegg.com - FSP Group BoosterX 3 FSP300-1E01 Max. 400W Independent/Supplementary SLI Dual GeForce 7900 GTX or Dual GeForce 7800GTX 512 MB CrossFire Ready Modular Active PFC supplementary Power Supply - Power Supplies
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My first suggestion is to download
EverestHome2.2personal or
PCWizard... and install. These utilities not only give more info than you could possibly want to know about your system, but also gives you real-time measurements of power levels and CPU temps. This is more useful for seeing fluctuations under load than in actual measurement of voltage values.
(One word of caution.... the temp and voltage values are only as good as your motherboards sensor readings... commonly a bios flash may be needed to correctly report temps...)
The ONLY positive way to get accurate PSU readings is to use a multimeter as outlined in the following link...
IMPORTANT - Testing Your PSU Rails - EXTREME Overclocking Forums Addendum...
After further exhaustive research, Ive found that even going to this length is virtually useless...
The precision and complexity of monitoring voltages is really far beyond that of the laymen...
The equipment needed is costly and uncommon... Better to simply buy good brands and read trusted reviews of people having used it under more strenuos circumstances than you...
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Most of us consider the power supply to be an option we simply check off when ordering a case, the higher the supposed Wattage the better.
The truth of the matter is, that it is at the heart of our systems stability, and the one component that can literally destroy all other components in our systems....
It can be at the root of problems ranging from random reboots, to poor performance in general...
Most people are surprised at just how much a PSU can make or break a system...
It is also an important aspect of OverClocking...
Without clean stable power, those voltage bumps are going to cause instability that you will assume is due to other parts...
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First thing to do is find out what power usage you will be working with....
The best way is to use
This website to calculate the maximum wattage your system could conceivably use at full load.
Remember that this is ALL components, at peak, all at once... not something that will ever happen in real world conditions.
Then add a little to allow for future power consumption needs, upgrades, mods, etc.
Total Wattage is not the most important concern by any means, however... Reliable brands, clean power, and Amp amounts on the main rails is much more important...
Your +12V rail is of the most concern for power users. It is what primarily powers most of the components...
Lower end PSU's usually have high +5V and +3V rails and underpowered +12V rails... (This "fluffs" up the overall wattage, which is what the average consumer looks at)
The issue of weight, when referring to quality, involves the manufacturer's use of heavier heatsinks, heavier gauge wires, more/better components to regulate power, etc.
A basic list of Good/Bad brands...
Good: Akasa PaxPower....... Antec
Astec.......................... AOpen
Channel Well.............. Coolermaster
Corsair........................ Enermax
Enlight......................... Fortron Source (Sparkle)
Gigabyte..................... HEC Compucase (excluding the lower-end Orion line)
Hi-Power.................... Hiper
Jeantech..................... Lian-Li
Mushkin...................... NSpire
OCZ Technology.......... PC Power & Cooling (now owned by OCZ)
PowerMan................... Seasonic
SilenX.......................... SilverStone
Tagan (ABS)................ Thermaltake
TTGI/SuperFlower...... Vantec
Xclio............................. Zippy / Emacs Verax
Zion.............................. Zalman Bad: A GBP Athena................ Allied
Aspire/Apevia............... Athena Power
Apex.............................. Athenatech
Atop............................... Broadway Com
CoolMax......................... Chieftec
DEER.............................. Dynapower
Eagle Tech...................... EYE-T
Foxconn.......................... KingStar
Inwin.............................. Linkworld
L&C ............................... Logisys
MGE................................ PowerMagic
Powertek........................ PowerUp
Powmax.......................... Q-Tec
Raidmax.......................... Rosewill
Skyhawk......................... Star
Startech ......................... Sunbeam
Turbolink......................... Ultra
It is not ALL inclusive, but does give you some general direction in ruling out the worst options...
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The following links will allow you to do more research and help you to comprehend Power Supplies and the role they play in your system....
Reviews... [H] Enthusiast - 450w-500w PSU Battle Royal EXTREME Overclocking - Powering Your PC: Truths and Misconceptions Article - Page: 1 - Tweaking PC Hardware To The Max Power Supplies 101: A comprehensive guide Motherboards.org RaidMax LP-6100D 400w Aluminum Blue General info... Why 99% of Power Supply Reviews Are Wrong | Hardware Secrets HEXUS.net - Review :: HEXUS PSU (Power Supply Unit) Roundup - Taoyuan 2005 : Page - 1/26 EXTREME Overclocking - Powering Your PC: Truths and Misconceptions Article - Page: 2 - Tweaking PC Hardware To The Max Choosing The Right Power Supply HowStuffWorks "How PC Power Supplies Work" Learn How To Diagnose Power Supply Problems - Otis F Cooper Ohms Law Calculation pcwiz inc Special Report - Bad PC Power, Power Supply Problems french press coffee maker match at leesspace.com Speedy 3D GideonTech.com Case Modification - Power Up an ATX PSU without a Motherboard How to choose an ATX Power Supply - PC Power Supply - How to Select Computer Power Supplies-Best Computer Online Store Houston Buy Discount Prices Texas-Directron.com ATX Power Supply Group Test Review - Peripheral Reviews - TrustedReviews
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Concerning
Ultra X-connects PSU's....
Now that some time has passed and more people have actually used and abused them, the consensus is that The Ultra X-Connects are not exactly the greatest... They are slightly better than a similarly speced
generic PSU... but I wouldn't trust them in a overclocking rig or in a power hungry setup, or SLI at all...
If you want a Very bling looking unit and your power requirements are in the low 300's, then these are fine I guess...
use at your own risk...!!
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DEALS
Newegg carries the Silverstone line of PSU's...
Newegg.com - Silverstone, Power Supplies, Power Supplies, Computer Hardware No-One but those running heavily laden SLI rigs will need more power than the 350 to 400 Watt versions
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Deals...
Don't know how long this will last, but NewEgg has an insane deal on a dual +12V Forton,...
Newegg.com - FSP Group ATX300-PA 300W ATX 12V (v2.2) Power Supply - Power Supplies
These have
OVER 30 Amps on the +12V rail...
These are perfect for smaller cases and simple systems that don't have a dozen HD's and extra drives...
They are also excellent as replacements for PC's like Compaq, HP, Emachines, etc., that use standard ATX PSU's
(specs here for verification...)
http://www.fsp-group.com.tw/english/...d=52&proid=182 
hardware
prices 
