I have had this problem with all of my laptops - the quickest way to get this fixed is to CUT OFF THE EARTH/GROUND PIN ON THE PLUG OF YOUR ADAPTER. I think they call this 'lifting' the ground/earth.
Don't worry about dying from an electric shock. All the new DELLS are plastic and do not conduct.
I have fixed the same problem on an HP, ACER and Dell laptop by doing this.
Good luck!
Vic in Sydney