Powerline can, but does not have to work. The 500 Mbit/s is a value from the laboratory and is anyway a gross figure that cannot be achieved in real life. In addition, the possible net data rate is much lower with Powerline than with a LAN cable.
https://de.wikipedia.org/wiki...
https://de.wikipedia.org/wiki...
Power lines are the worst possible data conductor and are only misused for this purpose by Powerline.
- Try other socket/s
- Use only the sockets in the wall.
A possible mistake was perhaps to take the cheapest models with 500 Mbit/s according to the motto "500 is enough...".
The models with a higher speed (>1000) have newer technology and can therefore possibly achieve a better result.