> Ouch. USB-C is even more fucked up than I thought… How does that even works with USB wall chargers?
If they want to supply more than 5V/3A, they need to support the power delivery protocol too.
> There are plenty of USB-A outlet everywhere (airport, trains, hotels, etc.), and most recent Android phones have only an USB-C port…
Exactly: These are USB-A outlets. These are possible to implement using only a resistor network to announce the maximum charging current and always supply 5V, which is much easier to implement than variable voltage and the power delivery protocol. USB-C can do this too, but only up to 5V/3A.
USB-C devices are usually backwards compatible with all three of these when using an A-to-C cable or adapter: Legacy USB-A current identification via the D+/D- pins, USB-C resistor-based current identification via the configuration pins of USB-C and USB power delivery.
If they want to supply more than 5V/3A, they need to support the power delivery protocol too.
> There are plenty of USB-A outlet everywhere (airport, trains, hotels, etc.), and most recent Android phones have only an USB-C port…
Exactly: These are USB-A outlets. These are possible to implement using only a resistor network to announce the maximum charging current and always supply 5V, which is much easier to implement than variable voltage and the power delivery protocol. USB-C can do this too, but only up to 5V/3A.
USB-C devices are usually backwards compatible with all three of these when using an A-to-C cable or adapter: Legacy USB-A current identification via the D+/D- pins, USB-C resistor-based current identification via the configuration pins of USB-C and USB power delivery.