If it is your mobile phone, which originally supports fast charging, it has now become slow charging, and there are two possible reasons for this.
One is that your data cable may be damaged in long-term use, generally in the place of the charging head, that is, poor contact and lead to slow charging, the method is to change a fast charging cable.
The second situation may be that the charging port on your mobile phone is damaged, you can change a jack, about twenty or thirty dollars!
The fast charging of the charger becomes slow charging, which is generally caused by the unstable loosening of the interface connection when charging, and the need to repair and check the tail plug board of the mobile phone to restore the fast charging speed