While your suggestion is along the right lines, keep in mind that computer power supplies are not like lightbulbs. They are spec'd to rate the maximum power they can produce to the device (and thereby draw). So, your 110W power supply is not drawing a constant 110W in the way a 110W light bulb would always being drawing 2x the power of a 55W lightbulb (all else being equal).

That being said, it is reasonable to assume that a PC with a 65W supply will generally use less power than one with a 110W supply, but much would depend on the use.