why consider watt of psu anyway

ruleworld

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since the amps required on 3.3/5v lines will never be a problem then why should we consider the total watt of a psu. a high watt psu will do no good if it have low amp on 12v rail. so isn't the amps on 12v the only thing we should consider when buying psu.
 

apt403

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Well the number of watts on the +12v rail corresponds to the number of total amps, the more watts, the more amps.

But yes, when your looking at your psu options the most important thing is how many amps there are on the +12v rail. Although its not like your going to find a 1000w psu with only like 5 amps on the +12v rail. Everything scales.
 

Aragorn

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Some PSU's have a high total wattage but have more amps on the 3.3 and 5v Rails than others, you can run into problems with those since computers use the 12v rails the most. I have never heard of a PSU that didn't have enough amps on the 3.3 or 5v rails.
 

tool_462

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I have never heard of one with not enough on the 3.3/5v rails, but some low end manufacturers shoot the amperage on the 3.3/5v through the roof to raise the total wattage while the 12v amperage remains on the low side.
 

ruleworld

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a 600 watt psu maybe better than a 700 watt one if it has more amps on 12v rail. for example

3.3v x 20a = 66w
5v x 12a = 60w
12v x 40a = 480w
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total = 600 watt , this have enogh power to run a 8800gtx


3.3v x 40a = 132w
5v x 40a = 200w
12v x 32a = 384w
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total = 700watt, but may have trouble running a 8800gtx

what i mean is since 12v is the only concern then totall watt should not be a consideration. only amps on the 12v matters.
 

stefx

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I have never heard of one with not enough on the 3.3/5v rails, but some low end manufacturers shoot the amperage on the 3.3/5v through the roof to raise the total wattage while the 12v amperage remains on the low side.

Do you have an example?
 

ruleworld

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I have never heard of one with not enough on the 3.3/5v rails, but some low end manufacturers shoot the amperage on the 3.3/5v through the roof to raise the total wattage while the 12v amperage remains on the low side.

Do you have an example?

PLENTY. just buy a 7$ psu.