Because fast charging requires agreement support, that is to say, the fast charging appliance you buy does not support your mobile phone fast charging agreement, the current domestic mainstream manufacturers of fast charging agreement is not interlinked, so you buy the wrong fast charging head that does not support the mobile phone agreement, it will fail.
The second is the need to activate, if your fast charging head is no problem, that is, the new charger needs to be activated, which is the first one or two charges will be slow, and then it will be fast, and the first few charges will be charged to 100%, which will be activated quickly.
Maybe it doesn't match the charging power of the phone.