Power adapters are a ubiquitous part of our electronics-laden lifestyle. A power adapter takes the output of one power source, like a 120-volt AC wall socket, and converts it to a different output, for example a 19.5-volt power supply for a laptop computer. Usually these devices work dependably and without worry. But if you find the electronics devices that you have connected to a power adapter are not working properly or that their batteries are not charging, there's always the possibility that the power adapter is not doing its job.
While running the laptop, pay close attention to the power indicator. If the power jack on the laptop is broken, the power may switch back and forth from battery power to AC power. This should be one of the first indicators of a problem. When the power adapter is plugged in, is the laptop charging the battery? If not, this is another red flag that the power jack is broken.
Set your multimeter to the proper range for measuring the output of your power adapter. Take into account the voltage and the amperage you'll be measuring. Consult the manual for specifics on how to set your particular model of multimeter.
Examine your power adapter. Every power adapter will have the input voltage and amperage requirements printed on it, as well as the output voltage and amperage rating. We'll be testing the output of the power adapter, so write down the specs.
Check the data plate of your power adapter to find out which portion of the plug is positive and which is negative. For example, on some power adapter plugs, the outer shell of the plug is positive, while on others it's negative. Touch the probes of your multimeter to the corresponding portions of the power adapter's plug and note the readout. Compare that with the rated output of the power adapter. If it varies significantly, replace the power adapter.
If you cannot get any power at all to your laptop via the power cord, try holding it at different angles while it is plugged into the DC jack. If this happens, save all important data before the computer becomes unable to charge and loses power.