Which were the first iOS devices to charge at faster speeds when connected to a 12W USB power adapter?
The iPad (4th Gen) was the first iOS device to support faster charging when charged by a 12W (2.4A @ 5V) USB power adapter.
The iPhone 6 was the first iPhone to support the same.
More recently the iPhone 8, iPad Pro and iPad Air (3rd Gen) introduced the even faster USB-PD charging.