# Measure the PSU Wattage?

The PSU I have reads 400W on the label. Its a cheap local one and has only 15A on its 12V rails, so I'm sure that its lower than indicated. Is there any way I can measure the real PSU wattage by any software, instrument, or any means. Please do not suggest kill-a-watt meter as its not available in my country.

• Do you want actual consumption, or rated maximum? Oct 29 '12 at 16:12
• What is on the other parts of the label? 15A at 12V is 180Watt. If there are rails supplying 220 watt via +3.3 or +5 volt then the label might be right. Having written that: 1) Outputting max 45% of the PSU's max rated power via +12v seems rather low. 2) To make thigs more complicates the output numbers added are often bigger that the maximum rated power. Meaning you can not draw the maximum from all rails simultaneously. Oct 29 '12 at 16:58

the watt rating is meant to be how much is can supply, not how much it will use under no load.

you could use a clamp meter to see the AC current consumption.

to measure how much it can supply, you need a calibrated variable "load". I have used 12V lightbulbs to do this in the past...

@Jook is right about the difficulties of testing the capacity of a power supply outside of a lab. It's expensive and potentially dangerous.

For real-time power consumption, if you can't invest in a Kill-A-Watt, you can try building a separated power cord that you can use with an inductive amp meter. These kinds of meters only work when you can measure the hot wire directly. If you put the hot and neutral wires both through the meter, they'll cancel out. (Explicitly measuring the hot line is basically what the K-a-W does.)

• The Kill-A-Watt is great for this, but his question specifically said that was not an option. Oct 29 '12 at 17:03
• @techturtle Ah! I didn't see that. I've expanded my answer. Oct 29 '12 at 17:10

If you want to know, what is the max my PSU could provide - I would say NO, there is no such thing, because you would have to actually use this amount of power until your PSU fails.

This would not be a good idea.