So now the retry with 200 Mbit Power-LAN. And what can I say: it works! Although only did the use of wall sockets properly (are power strips with other consumers in the way unsuitable for Power-LAN, better diekt in the wall!) Speed, then the connection is stable but with displayed 40 MBit / s. That I would not reach the promised 200 MBit / s was clear to me already from the experience with the first Allnets, but the actual speed is sufficient absolutely. The Internet has anyway only 6 Mbit, and copying files over the network comes with approximately 2 MB / s (16 Mbit / s) and fast enough. When two directly adjacent outlets I reached according Allnet software the way more than 170 Mbit / s.
So four star thanks to functioning properly, the Fifth is missing because of slightly incomplete documentation (scarce Manual: no recommendations for optimal connectivity that I had found in experiments themselves).