Questions about Samsung ECB-DU4EWE

if the S8 has micro USB then yes

I cannot charge my Galaxy S7 with this cable. Neither via the normal charger, nor via USB on the laptop, nor via the powerbank. I don't know what the problem is.

Hi Puma1973 This should fit - otherwise return it :) Type A is usually the wide, square connector used on computers. Type B is usually in a trapezoid shape. USB type C is then oval and can be plugged in on both sides :) Maybe this article will help you: https://blog.deinhandy.de/usb-typen-die-unterschiede-zwischen-usb-typ-a-b-und-c

Yes, it works with the white quick-charging adapter from Samsung.

Yes, I use it with my S7. The S7 has a micro USB port, the cable fits.