First check that you are using the original cable and charger. If the original data cable and charger are not used, the charging efficiency of the Red Mi K50 may not meet the standard. As a result, the charging speed of the mobile phone is slow.
Second, check if there is a problem with your phone's hardware. Xiaomi's phone has a built-in hardware for fast charging. If there is a problem with this hardware, then the phone will also be slow to charge.
The third is to consider whether the voltage where you charge is stable. If the voltage is low, the charging speed will also be slow.