https://www.bbc.com/news/articles/cdxv0ey94gxo

Lemme throw a wrench into everything. Sometimes faster charging can be better than slower charging.

Part of the USB power delivery spec is PPS or programmable power supply. PPS lets your device specify the exact voltage down to 0.02V or 20 mV. Heat is generated by inefficiency, and PPS’ goal is to get the voltage just right so there’s as little power loss as possible. My iphone charging at 5v 1amp “slow” charging gets hotter than the full 20 watts fast charging.

“slow” and “normal” are all relative terms, and aren’t definable.

It’s also relative to the size of the battery. A cell phone at 20 watts charging sure aint slow, but a laptop at 20 sure is. But is 20 fast when phones will do 50 or 100 watts?