Because now a lot of mobile phone manufacturers, charging. The standards are all different. If Xiaomi's charging system is not the same as Huawei's charging system, he can only achieve the minimum charging rate, rather than the fastest charging rate he has marked.
The same is true of other phones such as Opp and vivo. Only the minimum amount of charge that he specified. So charging will be slow.
Each company has its own fast charge agreement, Xiaomi charger does not support Huawei fast charge agreement, so it does not support fast charge, charging is very slow.
Because Huawei mobile phones have special chargers, which are specially configured and matched by the system
Xiaomi charge Huawei slow because the charging chip is not the same
The charger power is different, and the protocol is different