Originally Posted by
mike-wsm
Some good answers above.
What really worries me is that the OP proposes using a smaller power supply as a solution to the problem. This won't work. The computer will try to take the same power and the weaker supply will try to produce that power and will fail. You will know when it has failed by the burning odour, smoke, flames, explosion and fuslage rupture, followed by a calm weightless feeling as you achieve -9.81m/s2 vertical acceleration. Some time later you may briefly notice a splash or thump.
Never, never, never use anything but the correct supply from the original manufacturer.
Yes.....and no.
As I mentioned, Dell are pretty good in that their earlier 65W PSUs will power a laptop that comes with a 90W PSU but won't attempt to charge the battery at the same time.
Incidentally, the first link in FOR's Google search has a lot of useful info (that 110V @ 75W is the norm for planes).