It all depends on which power line you catch. The longer the distance between the power cables, the worse the signal. For this reason, it is worth trying out the setup at different sockets. This way I was able to get much more speed than at the beginning. -> Basically, there is always a loss of speed with this system compared to a direct Ethernet connection between router and PC.

Well, it has a Gigabit Ethernet connection, so it can't transmit more than that. I only have 50Mbit from my flat to the basement anyway...

The RJ45(LAN) can also be used for this purpose.