What power bank USB port to use to charge phone - 1A or 2.1A ?

Hello, how do I know which port on power bank should I use to charge mobile phone ? Do I have to plug the phone to 1A or 2.1A ? What is the difference between them ?

The difference between 1A slot and 2.1A slot is, that 2.1A slot provides more amperes, so it can charge your device faster. It may be explained: the higher the ampere, the faster the charging. But not all the mobile phones or other devices support faster charging.

When you are not sure if your mobile phone supports faster charging, it is recommended to use the 1A slot on power bank.

You have to be careful with using of faster charging of your device. Faster charging could harm the hardware parts when the device does not support it.