Interesting results using an app that measures amps coming from sockets.

[Gromett]

It's all based on what the plug supplies amps wise, rather than volts. It should say on it what amps it gives. If not it's watts / volts (12 or 240) = amps.

The USB charging system is a mess of different standards. The latest spec ones can set the voltage from 5v - 20v and can supply up to 5Amps.

Then there is the charging cables. I have a box of USB cables. Using the same phone and USB socket but only changing the cable I can double the rate of charge just by swapping a cable.

I prefer a slow charge overnight for my phone as it puts less stress on the battery and extends the lifespan.

This is a table covering the charging voltages/power. It is worth noting that the charge rate is affected by the device you are charging, the cable AND the socket you are plugging into.

USB - Wikipedia

en.wikipedia.org