Today I looked upon my desk: as you can see in the screenshot below, there are three plastic boxes containing A/C adapters for (I think all in the 12-20V and 1-2A range):
Altogether they are worse almost 2 kilograms metal and plastic.
My question is: are these dimensions already optimal, or could be same functionality put in significantly smaller size (like more than a half, or even 1/10?)
Or is this is by physics already mature technology which is not expected to improve?
Note: with keyword "feasible" I mean the fact that I understand that minituarization would cost more: "not feasible" means in this context like a 10-100x fold price increase.
The size (and weight) of these power adapters is always a compromise between price / size / weight. Yes they can be made smaller, especially with recent developments of GaN (Gallium Nitride) transistors, read more here.
These transistors are "better" switches than most of what is used today. Being "better" means less power is lost in the adapter and that means less cooling (area) is needed and size and weight can decrease.
As with nearly all new technology there is still a price to be paid, these GaN transistors are more expensive. Also the adapters need to be re-designed to take advantage of these new transistors. That takes time and money.
Not every customer and/or manufacturer cares about having a smaller power adapter. Would you be willing to pay for example $10 extra just to have a smaller power adapter?
So, first of all, cost is a very important factor limiting the shrinking of power supplies.
For example, an Apple iPhone and macbook chargers have relatively high power density (power going through the power supply per volume, in this case), but that came with a high engineering price, and expensive components and manufacturing processes.
Of course, there's theoretical limits. There's only so much power you can push through the magnetic core of a flyback transformer per time. More importantly, isolation distances still have to be kept to avoid danger.
Mainly, this is a question of using better controllers, higher-quality switching transistors and transformers to minimize size, along with investing more to make components withstand the larger temperatures inherent to reduced cooling surface.
As at least better controllers and switches are semiconductors, they still tend to get cheaper over time, and hence, more devices can economically feasibly have more efficient power supplies. Efficiency implies less needed cooling surface, so that might allow for smaller supplies over time.