Ok this is actually pretty hard to decipher but here’s the scoop:
- Apple finally supposed USB C Power Delivery. This means that with a USB C to lightening cable it can vary the voltage and amperage.
The shipped system is a USB A to lightening cable and adapter that charges at 5V at 1A so 5 Watts.
If you get the Apple USB C to lightening cable you should get the fastest speeds according to iMore which is strange but it is what test results show. Note that you need a direct connection to make it work.
The good news is that you can use non Apple chargers as well. Any USB C charger that is 29w or more should do a good job. So for your kit bag you want a cheap third party USB C car charger and USB C 29 watt charger. These can double as backup chargers if you have a MacBook 2016 or later. So the $59 Apple one has international compatibility with swappable plugs but if you don’t need it then the $22 iClever work well and is small.