Representative ATX 12 V. Power Supply Ratings (amps)

Power supplies vary in ratings by manufacturer and date of manufacture -- consequently, the power supply you have on hand may not exactly match the output ratings listed below. A power supply rated at 200 watts will be similar, but probably have slightly different amperage figures. I have noticed that the supplies of later manufacture tend to list higher current levels than earlier, but also list maximum combined output. Please keep in mind that the table below is approximate and is to be considered as a guideline only.


Model (Rated Output) 145W 200W 235W 250W 275W 300W 350W 400W 425W 475W
+3.3 V   14 13 13 14 14 28 40 40 45
+5 V 18 22 22 25 30 30 32 40 40 40
+12 V 4.2 10 8 10 10 12 15 15 15 30
-5 V 0.5 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
-12 V 0.5 1.0 0.5 0.5 1.0 1.0 0.8 1.0 1.0 2.0
+5 VSB * 0.2 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 3.5
+3.3V and +5V Max Combined Wattage **   135 W 125 W 150 W 150 W 150 W 215 W 300 W 300 W 300 W


* Standby voltage -- most system boards on recently manufactured computers will be constantly powered thru standby to allow for Wake on LAN startup.

** A little applied algebra will show that the total wattage (watts = volts x amps) produced would be considerably above the rated wattage of the power supply. However, recent manufacture power supplies will have a maximum wattage rating for the 3.3v and 5v lines combined. Even though you may draw up to the rated wattage from one voltage, you will not be able to draw maximum rated wattage from both lines simultaneously.

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