I’m constantly amazed by these things in daily life. The charger is just barely large enough safely house a USB jack, and that safety margin is large enough to

I’m constantly amazed by these things in daily life. The charger is just barely large enough safely house a USB jack, and that safety margin is large enough to fit a high-efficiency converter. If you are curious how it works, the Horowitz and Hill book, 2nd ed, has an extended section dedicated to describing how the power supply for the Apple II works. The iPhone uses the same technology, broadly speaking. Switch-mode power supplies were fairly new at the time, and older computers will generally use bulky, inefficient linear power supplies. Every once in a while I come across something from before the era of small SMPS, like a constant-voltage transformer that was bundled with my color photographic enlarger. The idea is that you regulate the voltage for the lamp to make the light color more consistent, but since the technology was old, it consisted of a massive, heavy ferroresonant transformer. I ended up selling it for scrap. The general way that you make power supplies smaller is by increasing the frequency they run at. For SMPS, this means increasing the switching frequency, but there are also some AC standards that run at higher frequencies in places where space and weight is at a premium. For example, AC power within an aircraft might run at 400Hz rather than 60Hz. The transformers are correspondingly smaller.