These devices now come in many different shapes & sizes, as well as features. Technologically, these devices are ever evolving, ever changing phenomena. Since many top brands are focusing their attention on producing better chargers, the prices are going down. Additionally, increasing demand is also playing a role in keeping the prices down.
Nevertheless, these wall chargers now come in stuffed with features. There are fast charging adapters, wireless adapters, pd adapters, 6 in 1 adapters, qc 3.0 adapters etc.
These external power supply, are usually in a case similar to an AC plug. Also, there are travel adapters, usb chargers and many more.
Now a days, phones have become especially sensitive to the charger used. Battery health, charging time etc depends heavily on the kind of adapter you are using. Different different phones having different charging technologies is playing the key role here.