You may need to test your laptop power supply (adapter) if your laptop does not power up. I will show you how to test your laptop power supply and what to look out for.

In order to carry out the test of your power supply you will need a voltmeter. You can buy a simple voltmeter for under 10 in any hobby electronics shop and all of the multipurpose ones will cover the voltage that we need to test for.

Digital volt meter

You can buy either an analogue or digital meter, my preference is digital and this pic shows that one that I bought from Maplins some years ago.

Next, you need to plug your laptop power supply into the mains!  

Many laptop power supplies have a small LED indicator on them which should give you an indication of whether mains electricity is reaching the supply,  if you know that your one does have an LED but it is not lit then it may be the fuse in the plug.  If that is the case then you can check the fuse with a continuity tester and you may well find that your multimeter has one.

If the LED is lit then proceed to the plug that normally goes into your laptop, carefully insert the tip of the red probe into the centre section and touch the tip of the black probe onto the barrel of the plug.

If for some reason the red probe tip cannot fit into the plug then you may need to use something like a paperclip... Just be careful.

If your laptop power supply is working then you will see a voltage displayed on the voltmeter.  In the case of this power supply it was 19.48 Volts but refer to the label on the side of your power supply as it will tell you the voltage that it should be producing. Most of the ones that I've seen are around 19.5 Volts.

If you notice that the voltage changes at all then you may want to test the cable. 

If you can manage to hold the power supply plug and voltage probes firmly in place, you can gently bend the cable backwards and forwards along its length.

It may be that the cable is breaking down inside which will lead to an intermittent connection to your laptop. You may also have noticed that the display on your laptop dims as it would have the effect of switching over to using the battery to run the laptop. If this is the case then a new laptop power supply will be needed.