You can, but it's best not to charge the iPhone X with a 45W charger. Although the iPhone X supports fast charging, it only supports chargers with less than 33W power. In the long run, it is easy to damage the battery of the iPhone X, which will affect the battery life. Try to use the 18W charging head to charge the iPhone X. For reference only
No, the phone battery does not support that fast charger, even if you use the maximum number of watts supported by the phone
Yes, the Apple X supports a maximum 18W fast charge, and the maximum power charged with a 45W charger is 18W