With many of us relying on our mobile devices it makes sense to have a spare power adaptor as a back up in case of problems with the original power source or because most of us carry a laptop between home and work keeping a power adapter in each location means that we have less gear to carry around and of course keeping a separate adaptor at work and at home saves us from the all too familiar anguish of opening the laptop bag only to find that we have travelled without the battery charger