Smartphones usually come with an AC adapter for charging. It plugs into an electrical outlet, and then plug the phone’s USB cable into the adapter.
The iPhone 4s has a really small AC adapter for USB-A, about the size of a walnut.
The Google Pixel 4a has a really big AC adapter for USB-C, about the size of a deck of cards.
Why is one AC adapter so much bigger? Something special about USB-C?