Use a multimeter.
An economical unit can be purchased for as little as $8 to $12.
Available in a multitude of stores. An auto parts store is but one example.
Analog or digital is fine.
The Red probe lead is the Positive lead. Plug it into the hole with the red circle, on the multimeter.
The Black probe lead is the Negative lead. Plug it into the hole circled with a black ring., on the multimeter.
The center knob is the Function knob.
Set it to DC Voltage.
If just a symbol is shown, set it to the dotted line over a solid line symbol.
If there is more than one DC Voltage scale, set it to the 0 - 50 Volt scale.
The plug of the AC adapter (Charger) that plugs into the laptop, has a center hole, and an outside cylindrical metal shell.
The center hole is Positive.
The outer cylindrical metal shell is Negative.
Positive probe lead to the center hole, then touch the Negative probe leads to the cylindrical metal shell.
You should be reading 19 Volts, or VERY close to it.
Also have an assistant gently wiggle this cable, while you are testing.
Have them wiggle the power cable TO AC adapter, also.
An intermittent reading indicates a broken wire, or wires. Discard AC adapter, obtain a good one.http://www.thelaptoppowersupplyshop.co.uk/advent-7021
The port on the laptop that the AC adapter (Charger) plugs into, is the DC Power Jack.
AC adapter checks out it's on to the DC Power Jack.
Post in a Comment if you wish to go on with the diagnosis.