It is possible to use 18W charging head with 20W wireless charger. The power of the charging head refers to the maximum output power, while the power of the wireless charger refers to the maximum received power. The power of the charging head only indicates the maximum output capacity it can provide and does not cause any damage to the wireless charger. Therefore, it is safe to use an 18W charging head to power a 20W wireless charger, but the wireless charger may not be fully charged or the charging speed is slower.
Basically there is not much difference in the power charger, it is a universal data cable, the plug model meets the premise.