@ Dunstan Vavasour: "transformers"
"Do laptops still have transformers? I thought pretty much all consumer electronics today has switch mode power supplies?"
This may be just a terminology problem. Switch-mode power supplies still contain transformers - just much smaller ones because you can get a higher energy throughput if you increase the frequency you send them from the 50 or 60Hz that's supplied by the mains. But I think the commentator meant power supplies generally.
Switch-mode *regulation* is the big efficiency gain - instead of getting the right voltage under differing conditions by a varying resistance, giving off a lot of heat (linear regulation), you only supply what's required by switching the supply on and off very quickly. Switch-mode power supplies do this inherently, but you can also add a switch-mode regulator to the output of a conventional transformer if you want. There's no point in doing this nowadays because the saving in copper and iron (with their associated space and weight) more than outweighs the cost of the high-voltage components needed to make a switch mode power supply. So everyone uses switch mode nowadays.
There is often quite a large scope for improvement in the efficiency of switch-mode power supplies by using more sophisticated designs, using more and/or more expensive components. As has been pointed out, the disadvantage of a inefficient supply, apart from its wastefulness, is its heat generation. The heat has to be got rid of. In a desktop computer it's cheaper to make a horribly inefficient supply and bolt on a fan to get rid of the heat than it is to make an efficient supply. Putting a fan in a laptop power supply makes it larger and less reliable, so these designs are more efficient to avoid needing a fan. Couple this with the efficiency of the laptop itself, both for battery life and heat dissipation reasons, and a laptop does a lot better than a desktop PC. By putting more laptop technology into desktop PCs (as is already happening with CPUs) you can get quite a gain for not much pain.