[EvaH (OP)]

Charles wants to know:

When charging a mobile phone you can use
A) Charger
B) Computer usb connector

Which is faster?

What do you think?

[syhprum]

This is a difficult question to answer by hunting for documentation as you need to know the voltage/current  characteristics of the two current sources and the charging current required by the device
Both charger and USB socket will both supply 5.0 volts and provided this does not drop when you connect the load there will be no difference in charging time.
It is not easy to measure this as you need some kind of breakout box or maybe just cut a cheap charge only cable!

[SublimeTC]

Charging depends directly on the battery and the usb wire used. Therefore, if it is possible to replace or improve them, then it is possible to speed up charging.

[syhprum]

The resistance of the charging cable is too low to have any effect on the charging current let no one be conned into buying a super expensive fast charging cable !, a £2.0  1 or 2 meter USB cable is more than adequate and paying more would not shorten the charging time.
   

[evan_au]

How can you make a mobile phone charge faster?

Don't let it discharge so far before you recharge it again...

[Bored chemist]

"How can you make a mobile phone charge faster?"
Use a smaller battery.
Obviously, you will need to charge it more often...

[alancalverd]

If your charger had zero impedance it wouldn't go any faster that the charging circuit in the phone will allow, since that is designed to prevent overheating.

Nikon provide a proprietary 1.5A cable with their camera chargers, and it is certainly heftier than the average phone cable.

A computer USB port must be able to supply at least 500 mA but there is no specified upper limit, and a remote hub dongle may be limited to less, especially if you are running several devices from an unpowered splitter.

In a word: there is no general answer to the question!

[Gawpchify]

In my experience, it is faster charging using with the adapter than using the computer usb connector.

[evan_au]

"Traditional" USB ports produced 5V DC.

Some of the newer versions of the USB standard allow a USB port to deliver 20V DC to compatible devices, delivering power up to 100W.

But I suspect that most phone batteries and charging circuits could not handle 100W, so charging will be limited to lower power levels.
See: https://en.wikipedia.org/wiki/USB_hardware#Power

[syhprum]

If we get 100 watt mobile chargers a time will come when they check the temperature of your mobile phone before you get on an aircraft much the same way they check you for COVID-19