system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Electrical engineers: What is the functional difference between DC and AC power?

 I understand the conceptual difference - electrons flowing one direction with DC and flowing in alternating directions for AC. But I am a coffee equipment technician and I've always wondered why equipment manufacturers choose to use DC power at all. For example some espresso machines use 24v DC solenoid coils, while others use 110v or even 220v AC coils to do the exact same work. Why? Any why are heating elements (as far as I have seen) always AC?

I'd prefer an explanation like I am five, but if there is a better sub for this question I can move it. thanks!
gpt
AC can be easily stepped up and down to different voltages with a transformer.  DC voltage regulation (especially boosting it up) is significantly more complicated, and until relatively recently it was impossible to do in an efficient and cheap manner.  This makes AC better for long distance transmission, as you can step it up to very high voltages, transmit it with low loss due to the lower current, and then step it back down to go into homes.  So that's why power coming out of your walls is AC.  Heating elements are usually AC simply because it works fine, and you don't have to convert anything.  DC is used in any digital electronics because those electronics communicate by varying voltages, and if your voltage is varying sinusoidally already you can't easily do that.  For your espresso machine, they may have already converted everything to DC, so it was simpler to make everything inside the machine run on DC.