Why does my laptop charger beep?
Some switching/regulated power supplies seem to have a hum or a whine moreso than others. (I've a Dell laptop supply that hums.)

You should try putting different loads on it. When the laptop is on, backlight at full, charging the battery, etc, the power supply will be under more load than when the laptop is powered off and the battery is full (or not present). Under the light load, the supply may hum more loudly or not at all.

My experience has been that if the power supply hums or makes noise when under load, it's probably an indication of impending failure. If it hums when under light or no load, it may simply be that it's making the noise as the switching circuit engages less often. (The Dell supply I mentioned hums under light/no load, and has been fine for years.)

A switching power supply essentially turns on and off at a high speed, and it is this cycling that can cause an audible sound.

Try the following:


Try a different wall socket. There might be a problem with mains power causing it.
Measure the output using a voltmeter to see if it's within tolerance of the stated specifications.


If it's a high-pitched whine or hum, it might be just fine. If it's more of a hiss or sparking sound, you might have bad components that are arcing internally, etc.

Most power supplies like this are very difficult to open up to inspect; not recommended unless you know what you're doing and don't mind voiding any warranty. It's probably best and safest to procure a replacement supply before doing any damage to yourself or your computer.

A related question: What component of my phone charger produces chirps and how does it do that?