Understanding iPhone Air charging
The iPhone Air reaches 20W only when the charger, the cable and the phone agree on the same fast-charging standard. An old USB-A cube or a cheap gas-station charger falls back to about 5W, which can make a full charge take three hours or more.
iPhones use standard USB Power Delivery, so any quality USB-C PD charger of 20W or more reaches full speed. More watts than that won't charge the iPhone faster, but it's fine to use.
Do you need a special cable?
Any good USB-C to USB-C cable rated 3 A (60W) handles full speed.Check yours with our USB-C cable checker.
Test your charging
Compare other chargers with the charger compatibility checker. If charging keeps disconnecting, run the full phone diagnostic to test the charging port, and remove lint from the port with a wooden toothpick.