And now power supplies are getting another step smaller and more efficient by switching from silicon transistors to GaN. ( https://www.cui.com/blog/how-gallium-nitride-gan-enables-sma... )
It surprises me that GaN marketed power supplies cost extra. The actual GaN transistors are under 10 cents now, and by using one you can use a smaller inductor, smaller capacitor and smaller heatsinks. Those smaller components lead to a smaller plastic case and smaller circuit board. All of those smaller things cost less, so the finished product has lower production costs.
The ones I've bought haven't been terribly expensive. About half the price of Apple chargers. I daresay you don't want to go too cheap with chargers as they can overheat/pack up/damage things.