Saved. PSU replaced the original well.

During a call, my almost 6-year-old Fritz box 7170 went on strike. In order to put it back I have separated for a brief period of power. This has always helped in the normally highly reliable Fritz box, if it does sometimes made bitches. I noticed this time that the power supply was extremely hot. The Fritzbox read no longer bring the reinserting the power supply in transition. The LEDs only blinked in a difficult nachvollziebarem scheme by succession.
Since I was now not only without phone but also without DSL, I had to investigate with the smartphone on the Internet, what could be the problem. Here I found in forums the info that is not the Fritz box itself must be the problem, but after a few years, the power supply may be defective, even if it similar to mine, still indicating 12V output voltage with a meter.

When searching the internet I found this inexpensive replacement product.

Description:
The power supply is of a size approximately the same length and the same width as the original power adapter by AVM. However, it is almost twice as deep. The cable is about two centimeters shorter and has built a thick round device near the connector part in the cable. The original cable does not have this component.
The output current is 0.3A to higher than the original (1.5 vs. 1.2 A).

When using this power supply, the Fritz box has immediately resumed the service and now after a few hours the power supply is barely more than lukewarm.
Anyway, I am glad that with this power supply again everything works and hope that even many years to come.