One of the most frequently asked questions in the forums is "Wich power supply should I get?"

This is an area of great confusion, and I am not on Mr.Satan here, but this quote below from another thread (And similar statements I have seen over the years) prompted me to reply to it, and what started out as a semi-quick post suddenly turned into a lengthy reply.. so I thought it deserved a FAQ/Guide onto itself

Quote: Originally Posted by TheGreatSatan $200 to $400 on a PSU??? Stupid

Is that kind of power supply neccesary for a mild build up with no overclocking?

No, power supplies that are in the 50-75$ range with 300-350 watts will be generally be fine if it is made by a well known company with a good track record like Antec.

How about a midrange computer with a mild Overclock in mind?

Not likely, it's probably overkill.. something in the 450-550 watt and the 100-200$ range will likely be plenty

What about a high end build with SLI or X-Fire and heavy overclocking?

YES! When you are living large and have spent lots of money on the latest and greatest hardware, this is not an area you should be thinking about trying to save money in...650-1000 watts is what you should be looking at , they tend to fall in that 200-400$ range.

Notes:

I have an Antec 300 watt smart power that came with my gaming rigs Antec case, and it works fine for a low end Athlon XP/ AMD 64 and a midrange video card..until you try and Overclock it...then it falls way short of its potential compared to the 550 watt Antec True Control I normally use.

CPU's like the "Prescoot" based Pentium D dual core will draw quite a bit of power, so anything that sucks a lot of juice (Amps) would not be a good idea with 300 watts...look more in the 350-400 watt range as a minumum..even without overclocking!

The minumum power supply I like to see anyone use for a decently equipped rig that may see some overclocking or is equipped with dual video cards generally needs at least 500-600 watts, you always want a bit of headroom so the power suppply does not have to run flat out all the time, wich can lead to a premature death, and unstable performance in a hot environment.

Tech:

Now I don't have time to get into all the details of a power supply, but "Ripple" is one area that is very critical to stability, the X-connect is a prime example of a realy bad design that has lots of ripple, and is part of the reason they die early and/or can kill hardware over time. Smooth and steady is the rule here, that will keep all your sensative electronics happy!

Here is a chart that will make it painfully obvious as to why you don't want to cheap out and get a generic or low end power supply!


One measure of a good power supply (Though by itself is not definitave) is the weight.

A cheap 20-50$ 500 watt supply will seem light as a feather, where a PC Power & Cooling at the same 500 watt level feels like you are holding a brick!

The high end power supply use much heavier duty components like the Capacitors, and use pretty massive heat sinks to keep everything cool (The reason they tend to be so heavy) those are areas where the cheap ones skimp on to save money.

The other "Trick" that cheap power supply makers use it to "Artificially" pump up the power ratings.

They have high realy high amperage going to the 3.3 and 5v rails, while the 12v rail will be on the wimpy side..and the 12v rail is what power the most critcal items like the CPU and video card, unfortunately the total wattage is all people typically ever pay atttention to!

My OCZ 520 SLI has the following ratings, and is one of the most potent around at a decent price..it has served Digital World and myself in our high end multiple video card rigs with honor

+3.3V(28A),+5V(40A),+12V(33A)
http://www.ocztechnology.com/product...idia_sli_ready_

Now if we go with a under 50 buck 500 watt power supply look at the specs..especially the 12v amp rating

+3.3V(35A), +5V(61A), +12V(28A)
http://www.newegg.com/Product/Produc...82E16817104123

Notice how high the amp ratings are in areas that don't realy matter? They are both in the same 500 "Wattage' rating category..but will perform very differently in your PC under a heavy load.

Here is a realy good article on exposing "Myths" about power suppies, and how they rate them..it's a must read!

http://www.pcpowercooling.com/technology/myths/

Power supply roundups:
http://techreport.com/reviews/2004q4/psus/index.x?pg=1
http://www.xbitlabs.com/articles/oth...u-roundup.html
http://www.pcstats.com/NewsView.cfm?NewsID=45331

600-700 watt shootout
http://www.pcstats.com/NewsView.cfm?NewsID=52698

SLI power supply roundup
http://www.pureoverclock.com/review.php?id=15

This last article below is about using dedicated mini add-on power supply, they will allow you to keep your current 400-500 watt power supply, and power up those hungry multi card set ups keeping them very happy without ditching what you allready have.

http://www.pcstats.com/NewsView.cfm?NewsID=52586

Overclockers will realy love them too, they are the newest hot trend for the "Extreme" crowd too...I would love to try it them out one day myself!

One area I did not touch on is the Single vs. Dual vs. Triple vs.Quad rail debate..I wil try and add this later, but dinner is ready, and I am gonna get my butt kicked by Pimpette if I don't get it now!

Here is a link to NVIDA SLI approved power supplies:
http://www.slizone.com/object/slizone2_build.html


EDIT: I am adding a link to the PCApex PSU calculator, it even includes the ability to add Overclocking to the estimate power calculation!

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this fully and helpful guide for the power supply this help me a lot thanks $SOLID$ Necro thanks and good luck with you

I'm glad you wrote this .
It's like banging your head against a wall trying to explain why 2 PSU's of the same "Watt "rating are vastly different. (Amps on the12V rails,not total watts!!!)

Also heres another twist some new power supplys with independent rails can fuse them all together at high loads.
Example= the "Mushkin 650" with 4 seperate 20 amp 12volt rails will combine them at high loads for Uber SLI setups.

http://www.mushkin.com/doc/products/...ply/xp-650.asp

And heres another VGA power supply,"Fortron Booster X3" 300 Watt VGA power supply.
http://www.home2000.net/client/fspgr...linenumber=230

Nice guide Solid as always

Excellent guide and links.

Other factors to consider are heat, dirt and quality of your AC line coming in.

A line conditioner and/or UPS can help out with the latter.