The Power Supply FAQ. Please read before asking your PSU question!

[Steve]

I am a firm believer in the importance of a good PSU when using a graphics card in your system.
Why would anyone want to connect an untrustworthy or insuficient power supply to their brand
new $300.00 video card? Well hopefully after reading through this FAQ you will be armed with enough
knowledge that you will never have to worry about your PSU destroying your expensive components.

Table of contents:

Post 1
Intro
Table of contents
Wattages and rails

Post 2
Brands

Post 3
Neato PSU features
ATX/BTX
Connections

Wattages and rails

What are Watts?
PC components consume power in the form of Watts. CPUs, hard drives, video cards, optical drives,
fans, 12V water cooling pumps all rely on the PSU for their power needs.

Every power supply out there should tell you how many Watts of power they can provide and sustain.


How many Watts does my system require?
This is going to vary depending on your specific components. First I am going to start of with
general "rules of thumb".

When you look at the retail box of current nVidia and ATI video cards it should list the Wattage of
power supply that is required in the "System Requirements". Usually they only tell you what you need
to run the single card in the box even if the card can be used with SLi or CrossFire.

These numbers take into account the average PC as well. This means that if you have a very power
hungry CPU and more than 2 hard drives, 2 optical drives, 4 case fans and a 12V water cooling pump
you may want to get a power supply with about 20-30 Watts more than what they suggest.

Below I have listed the most common PSU requirements by Wattage and the single graphics cards that
require that amount of power.

250 Watts or greater
MX 4000 PCI
FX 5200 PCI and AGP
FX 5500 PCI and AGP
X300 SE

300 Watts or greater
Ageia's Physx Physics Accelerator
6200 PCI and AGP
6600 LE
6800 (18 Amps)
6800 XT (18 Amps)
7300 GS (20 Amps)
7600 GS (20 Amps)
9700 Pro
9800 series
X700 series
X800 series
X1300 512MB

350 Watts or greater
6600
6600 GT
6800 GS (18 Amps)
6800 GT
7300 GS PCI
7900 GT (26 Amps)
X850 series
All In Wonder 2006 Edition
X1300 Pro
X1600 series

400 Watts or greater
7800 GS AGP (20 Amps)
7900 GTX (26 Amps)
X1900 GT (25 Amps)

450 Watts or greater
X1800 XL
X1800 XT
X1800 CrossFire Edition
X1900 CrossFire Edition (30 Amps)
X1900 XT (30 Amps)
X1900 XTX (30 Amps)

600 Watts or greater
7900 GX2 (two pcbs)
7950 GX2 (two pcbs)

Below I have listed the most common PSU requirements by Wattage and the dual graphics card setups
that require that amount of power.
Here are the links to ATI and nVidia's certified PSU lists:
nVidia's SLi certified PSUs
ATI's CrossFire certified PSUs

400 Watts or greater
6600 SLi
7300 LE SLi
7300 GS SLi
7600 GS SLi
X300 CrossFire
X600 CrossFire
X700 Pro CrossFire
X800 CrossFire
X800 GT CrossFire
X1300 CrossFire
X1600 XT CrossFire

430 Watts or greater
6600 GT SLi
7600 GT SLi
X800 Pro CrossFire
X800 XL CrossFire
X800 XT CrossFire

450 Watts or greater
6800 GT SLi
7800 GT SLi
7900 GT SLi
X800 XT-PE CrossFire
X850 XT CrossFire
X850 XT-PE CrossFire
X1800 XL CrossFire

550 Watts or greater
6800 Ultra SLi
7800 GTX SLi
7900 GTX SLi
X1800 XT CrossFire
X1900 XT CrossFire

600 Watts or greater
7800 GTX 512MB SLi
X1900 XTX CrossFire

850 Watts or greater
7900 GX2 Quad SLi
7950 GX2 Quad SLi
Note: VoodooPC uses a 650 Watt PSU built by them for their Quad SLI system and Falcon Northwest
uses a Silverstone 600 Watt PSU for theirs. If you ask me that is not enough, but if it works I guess
that's fine. Alienware uses a 850 Watt PSU built by them.

If the "rules of thumb" do not apply to you because you have more or less components
in your system you should try using this wonderful Wattage calculator.

eXtreme OuterVision's eXtreme PSU Calculator v1.3

I like it because it lists tons of new and old video cards and it is very up-to-date.


What are "rails"?
"Rails" refer to the different voltages that a PSU supplies. They include the 3.3V, 5V, and 12V lines.
The 3.3V, 5V and -12V lines are connected to your motherboard inside that groovy 20 or 24 pin connector.
The +12V line(s) power all your hard drives, optical drives, graphics cards and any case fans not
connected to your motherboard.

Unless you are getting a high range video card or you are going to have a SLi/CrossFire setup you should
look for a PSU with at least 25 Amps on the +12V rail. Of course getting a PSU with more Amps wouldn't hurt!
If you are going to get a high range video card or a SLi/CrossFire setup read the requirements of the cards,
but you will need something over 30 Amps.

These specs were taken from PC and Power Cooling's and Enermax's websites. The areas boxed in red
tell you how many Amps are on the +12V rail for the 1,000 Watt PSU from PC and Power Cooling
and the 620 Watt Liberty from Enermax.



Nowadays power supplies may come with 2, 3, or 4 +12V rails so be careful when the specs proclaim
something outrageous like "60 Amps combined" on a PSU with 4 +12V rails. It may be true but only two
of the rails are for your graphics cards. The other two are for your CPU.