How To Test A Laptop AC Adapter
You have a Laptop Computer that will no longer power on. I generally would find that either the dc jack was damaged or the laptop ac adapter no longer functioned. If you suspect the dc jack, then you are going to disassemble the laptop in order to visually inspect the dc jack. The problem was usually due to the lead from the dc jack to the motherboard being broken. This requires removing the motherboard, de-soldering the dc jack and installing a new dc jack. This best done by a computer service center.
If it's not the dc jack, then it may be the motherboard or the laptop ac adapter. Okay, so to test the ac adapter, you are going to need a good digital multi-meter. These are easily available on either Amazon or Ebay and they vary in price. The other thing to do, is to inspect the cable from the electrical plug to the ac adapter ( also called the brick). I would also touch the brick, to determine if it is getting hot.
If it is not hot and the cable does not look chewed, then you need to test the ac adapter with the digital multi-meter. This can be a little tricky due to trying to hold the ac adapter barrel plug end and the digital multi-meter probes. You will need to plug the ac adapter into the wall plug. Now hold the black negative probe against the silver metal outside shield on the plug. Then place the red positive probe inside the plug tip. Do not touch the the plug going into the wall outlet, because it is 120 volts ac voltage and will electrocute you. The end you are working with that plugs into the laptop is low dc voltage and will not hurt you.
There may be a problem if the red positive probe tip won't fit inside the barrel plug. I have found that you can place a metal paper clip inside the barrel plug. Hold it firmly so you make a good connection. Then take the measurement. Again, you may need a second person, because you only have two hands.
Make sure you have the digital multi-meter set properly to read the output dc voltage. If the reading is good, try moving the wire connected to the barrel plug in different directions. If the voltage is good and then bad, you have a broken wire. You may want to have a second person to help you with this as it can be tricky to hold and move the wire.
If it is damaged, you can try cutting and replacing the barrel plug. Just make sure you have the correct barrel plug, because there are different types and sizes. Plus it depends on where the break in the wire occurs. 99% of the time, it is best to just replace the laptop ac adapter with a new one. If the ac adapter is getting hot - replace it.