Power supply efficiency

[Braeden Hamson]

I was looking at this here power supply,

https://www.amazon.com/Generic-Replacement-Adapter-Inspiron-19-5V-3-34A/dp/B003U8HV4M

It outputs 19 V at 3.34 A for a Wattage of 65W. Input is (Lets say) 120 V at 1.2A, I think the power there is 144W. Does this mean that ~80W is wasted, and that the supply is 44% efficient?

Thank you,

-Braeden

 

[AnalogKid]

No. A supply of that type usually is around 75 to 80% efficient at full load.

The 1.2 A input current is a way overestimated estimate. It might be the startup inrush current, bit it seems low for that.

ak

 

[Braeden Hamson]

Thank you, your post encouraged me to not trust ratings. I just tested the efficiency of my laptop's power supply. Which was a somewhat hazardous affair with a tangle 120 VAC alligator clips running between the plug and my multimeter. While charging my computer the charger drew 0.5 A from the wall. The case says 1.5 A. on the DC side its 18.5 V I couldn't measure amperage, I didn't feel like shoving my meter leads into the laptops power socket lest I short the charger pins. So I guesstimated that it runs at 2 amps as its rated for 4.2 A peak. This gives it an efficiency of 77%, right on the money.