In a datasheet, Apple reveals how it works and there is reason to be a little disappointed (but not really surprised):
• If you connect a laptop and an iPhone or iPadeach device receives up to 17.5 W.
• If you connect an iPhone and an iPadeach device receives up to 17.5 W.
• If you connect a Mac laptop or iPhone and an Apple Watch or AirPods, laptop or iPhone receives up to 27.5W and Apple Watch or AirPods receive up to 7.5W.
Clear, unless you only plug in very small accessories (AirPods, Apple Watch), even a MacBook Air will have very low charging power and at best, you’ll just keep it in its current battery state. It is therefore better to opt for the chargers that were recommended to you at the time of its release: