Do you mean that I should be ok using a 12volt 2 amp transformer for my g scale.  Will therein move?

I have two Big Haul sets, a liberty bell and a Blue Comet.  Both came with 20 pieces of track and a 17 volt transformer.  I would like to add a gondola to carry a small toy for my children and expand the track. That appears to strain the 17 volt Lifelike, tyco, bachmann transformers.  Any suggestions as to how i can get more power to the track?