I tapped on interference made me smart online and came across this Fritz! Series encountered.
"With integrated mains filter for the best possible data transfer ..." but that sounded fine and Fritz! is indeed quality (I have the 7390 and 7270 in use) - I have these 546E powerline adapters ordered (in conjunction with 520E).
The installation went smoothly and actually analogous to my TP-Link Kit - then the surprise!
Even the Fritz! Powerline breaks completely together after plugging the computer.
Neither a more stable connection even better than with the TP-Link kit!
So I ask myself; what for the filter function please ???
Conclusion:
I do not want to generalize my experience but for me is also the Fritz! Powerline completely flunked.
Powerline is just no completely reliable system, you have to be lucky and the right "environment" have it.
For me is not an option, I'll stay at the LAN cable!