Apex domains cannot have CNAME records.
Question and response
Question
dig powersrv.de. NS
Answer
powersrv.de. 5 NS third-dns.netcup.net.
powersrv.de. 5 NS second-dns.netcup.net.
powersrv.de. 5 NS root-dns.netcup.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0