No, Xiaomi's k40 can not use a 120-watt charger for fast charging, but the 120-watt charger can be adapted downward, Xiaomi's k40, he only supports 30 watts of fast charging, if your power adapter also supports 30 watts of fast charging, then he can charge Xiaomi's Redmik40. If your charger also does not support 30 watts, then she will be adjusted downward, charging power will be lower.