Raspberry Pi: why can't Ethernet work?

Question

Raspberry Pi

On the Raspberry Pi 1 Model B+ (512 MB), the network adapter does not work in any way: the lights on the adapter do not blink, the light on the router does not blink. I tried different power sources, different network cables, tried to connect to a computer (just to check if the signal goes through). Nothing.
At the same time, the network works fine with the Wi-fi adapter. Why can this be?
At the moment, a network adapter with a declared current of 2 A at the output is used.