The label of the mobile phone charger says the output voltage of the charger, usually 5V, and there is also a dual engine output voltage, generally 9V, and the charger with the output voltage of the dual engine will have a special identifier.
The charger will also mark the charging current, such as 2A or 1.5A, some flash charger marked with 4A charging current, the power of the charger is the charging current x output voltage, the unit of power is watts (W).