(I'm going to try to be as non-argumenitive from here on out, so bear with me)
The Wiring in almost all power supplies is 16ga, with some wires such as 5vsb/-12v/psu-on being smaller gauge (no more than 2-3 amp over the wire). You may verify this yourself by checking any psu's you have against eachother. Some units may have higher than that but I have yet to hear/see/read a review of anything with high gauge wire being noted. Not even the PCP&C psu's have more than say 14ga (which still cannot carry the psu's full amount of current).
(Heres my contributions to the guide)
Power supply ratings - The reality of Watts
Every consumer power supply today has a output rating in watts. Some are the absolute maximum they will output before overload, and some are the normal continuous output.
When it comes to buying a power supply there are several things you want to pay attention to other than just the wattage. Number one is the brand, as a 1000w psu from one company may be a waste of money vs a 750w from another company. Second is efficiency, which I will outline later. Lastly you want to look for PFC or
Power
Factor
Correction, Modular/Non, Silent, Asthetics.
All of this wattage business generally confuses most people, as logic would tell you more is better although that isn't always the case. In terms of wattage the main thing to look for is the total number of +12v Amps. This is where the "more is better" mantra rings true. Finding that number for any given power supply (referred to as PSU from now on) can however be a slight challenge.
Take my psu for example. I have a OCZ 700w GameXStream psu (NewEgg link
http://www.newegg.com/Product/Product.aspx?Item=N82E16817341002).
According to its specs it produces 700w (unknown if max or continuous) and the specified current for each voltage:
+3.3@36A (118.8w)
+5V@30A (150w)
+12V1@18A (216w)
+12V2@18A (216w)
+12V3@18A (216w)
+12V4@18A (216w)
-12V@0.8A (9.6w)
+5VSB@3.0A (15w)
Already you should start to notice that if you add all of those up you are well over 700w and above even 1000w. If the psu output those kind of numbers all the time it would produce 1157.4w, so something has to be up if it is only a 700w unit.
That answer is a current limiter. These are placed in several areas in a psu to prevent overloading a wire to prevent damage or fire, or to prevent overloading the transformer and burning it out. Some of these limit by amps and some limit by watts. While these maximum numbers say the unit is capable of over 1000w the limiters prevent that so you cannot overheat the psu. According to the sticker on the side of the psu this is how the numbers break down.
The combined output of the +3.3v and +5v is < 155w, combined output of all +12v is <50amp or 600w, combined output of -12v and +5vsb is 20w. Combined +3.3v, +5v, +12v must be under 680w, total output <700w. Maximum amperage is 70amp.
This may seem complicated but it describes how these limiters are setup inside this unit.
Now that we have the wattage explained lets talk about finding the correct psu for your computer. Say the computer in question uses roughly 500w full load, with no overclocking. The general rule of thumb is that your computer should only use about 75% of the psu's capacity. This way you have prolonged life of the part, less heat and noise, better efficiency, and overclocking/upgrade headroom. So that means for your 500w computer you would want a unit between 650w and 675. Any psu above 400w should have at least 5/8 of its power on the 12v rail so 650 X (5/8) = about 400w / 12v = 33amp.
Next you want to narrow your search down to 650w+ units with at least 33amp of current on the 12v rail. Here is where things start to get very interesting - 12v rails. One rail, two rails, three, five, which is right for you? All normal sized psu's have a single transformer that takes the 110v/220v from the wall and turns it into dc. From there the current is changed into 3.3v, 5v, etc. With todays power supplies having so much current on the 12v rail some strange things were starting to happen. Motherboards started pulling so much current that the wires would melt, causing fires or at the least frying the power supply. As part of the ATX12v spec limited rails were introduced to prevent this overload from happening. This spec required a limit of 18a over any one 12v output. Most psu's have 16ga wire, which at the most can supply 22a of current before overheating and melting the wire.
You are wondering why I just gave you the history lesson, well that is how the multi-rail power supply business started, as a safety spec. Now it just adds more confusion for consumers. What you want to look for is the total output of the rails, not simply 18a times the amount of rails. For this OCZ the max for all rails combined is 50a. Other units may not list a maximum.
That is all I have time to write for now, I need sleep.
