Another factor that comes in play that most don't think about is the electrical outlet you are plugging into. (this goes for your home outlets as well) Depending on quality of the outlets over time they begin to wear to the point they do not grasp the blades of your male plug properly. Thus high resistance.
There are two type of male blades on plugs. One is a solid blade and another is a folded blade that can be opened with a thin screwdriver or knife blade to make it fit tighter. On the solid blade type I've tried placing a slight twist on the blades with some success.
The dogbone type is better though if the 110v plug isn't a 90 deg type you can help to offset the weight of the cord with zip-ties.