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Equation for a power supply?

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doesnotcompute

Registered
Joined
Feb 28, 2003
How do you calculate the wattage of a power supply's 3.3 and +5 lines if you are only given the volts and amps? I hear that the max values listed on the power supply are not the correct values for determining the total useable wattage of the power supply. If that is true, than can anyone help me by telling me why.
 
I don't think you can get it from those numbers because they aren't related that closely to the combined power:

Powmax: 28A @ 3.3V + 30A @ 5V = 242.4, combined 180W

Delta: 26A @ 3.3V + 32A @ 5V = 246W, combined 245W

Antec SmartPower: 20A @ 3.3V + 30A @ 5V = 216W, combined 220W (probably rounding error)

Maxpower: 14A @ 3.3V + 30A @ 5V = 196W, combined 190W (verified, but only after extra diodes added to +5V)

Notice how the PSU with the highest calculated total here had the lowest combined power rating.
 
Thanks for the info. I just gutted my other system and installed that power supply and the rebooting has stopped.

My first PSU 400Watt 3.3 = 14A 5=30
My new installed PSU 300Watt 3.3=20 5=30

Can you believe that or explain that?
 
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