When you unplug then plug it back in you are resetting the adapter. The fact that you have to do that definitely points toward a short of some kind. You could try another adapter but I would bet that either the DC jack has a short or more than likely the MB is the source of the short. So 1st try another adapter and if the problem remains then replace the DC jack. If that does not help then replacing the MB is your next step.
There is this confusing issue with my laptop vostro 3491 that as soon as I insert my charging pin in my laptop, the green light on my 45.0W adapter goes off.  And the laptop doesn't charges either. Before plugging the pin: [IMAGE] After plugging the pin: [IMAGE] Please tell me a solution to resolve this problem. And the main thing is this problem arises one day and then doesn't on another. I am fed up with this problem occurring every now and then.
Charging issues with vostro 3491