As my first Raspberry Pi catched some dust I found a new project involving it.
Researching current procedures regarding backup old image and add new image to the SD Card, here it is:

Backup

• Putting the SD Card in my reader in my Mac
• Utilities > Disk Utility
• File > New Image from boot
• Choose as type CD/DVD image and save it

New Image

The really cool and minimalistic tool Etcher is suggested by the RasPi homepage.
I chose the current Raspbian 9 to be put on the SD Card by Etcher.

Etcher in use

Once the copy/install process was finished I opened a terminal session, navigated to /Volumes/boot and used touch ssh.

This will enable ssh on the RasPi, directly enabling it to be contacted by a terminal session instead of putting a usb keyboard on it.

• User: pi
• Password: raspberry

Any changes can be done with sudo rasps-config – especially password and network name of system

Now the old RasPi can be used again, this time without extra ac plug but on the new Bestek Steckdosenturm.