Can I use 18w charger type-c from iPhone 11 Pro on iPhone 7?

if one use a usb-c to lighting converter

because as long as the connector fit the ios device and the volts are not higher than 5

and the charger can provide a minimum of current of 0.5 for non ipads and 2.4 for ipads

watt == Volts * Current

current == Volt / resistance

(Ohms law)

the resistance is controlled by the ios device in question so it will not pull more current than it was created to be

so there really is no max for how many watt the charger is able to provide, as the ios device will pull was it was created to charge by.

any charger that has the correct connector and does not output higher than 5volts can be used

without harm