Man, I wish self hosted email was a reasonable thing to do. But it’s a pain to set up the server and the domain stuff, and once you do, if anyone ever spammed off that IP, you’re probably screwed anyway because good luck getting off the blacklists.

A Coulomb is basically a number of electrons, so it still very much depends on capacity. The only way it could avoid capacity dependence is if the amperage varied depending on total available uncharged capacity. That in itself is unlikely because the wires that transmit the electricity can only handle so many amps before getting too hot and melting apart, so any charging system must necessarily be constructed with intended charging capacity and rate in mind from the beginning.