I know that a rule of thumb to judge the efficiency of a traditional iron core transformer is to look at its size: the larger it is, the higher the number of windings, the larger the core, the ticker the wires... All factors that in the end lead to lower energy losses and higher efficiency. (Or maybe I should say the other way around: a requirement for a transformer to be efficient is to be large.)
But what about modern switch-mode adapters? Empirically, I can feel that small adapters heat up very easily, even with low loads, while larger adapters don't heat up much (if at all) even with high loads. This could be because larger adapters disperse heat more easily, but it could also be because they're truly wasting less energy.
Hence the question: assuming the same load, same input wattage and same output voltage, would a larger switch-mode adapter be more efficient than a smaller equivalent?