Note: this is not about a specific device but the general aspects of charging a USB device using accessories with different USB standards so I hope this fits here.
I've got a Samsung Galaxy Smartphone with a USB 2.0 Type C charging port.
Using the stock Samsung wall plug (9 V, 1.7 A output or 5 V, 2 A fall-back) and charging cable (USB A to C) the device gets charged utilizing Samsung's "adaptive fast charging" technology.
Using the included charging cable with a generic USB A wall plug without Power Delivery (5 V, 2 A output) nets a very slow charging speed of approx. 900 mA. Incidentally the same current as specified for USB 3.0 ports.
The same exact charger and a regular Micro USB cable would charge any old smartphone with a maximum of 2A sans utilizing USB-PD. Why doesn't it work with the OEM Samsung USB A-to-C cable? The USB 2.0 specification also states a maximum of 500 mA and every charger in the last years exceeded that. The Samsung device doesn't even have a USB 3.0 port, it's just USB 2.0 with a Type C connector.
I'm trying to understand this from a technical viewpoint. Can you point me into the right direction? USB 3.0+ and Type C is honestly pretty confusing.