You are right, I confused the word current with voltage, I am sorry. Please replace every "current" in my posting with "voltage".
if you have another suitable dc power supply
I have ordered a new power supply with fixed steps of the output voltage. And also a breadboard for more serious experimenting 
Now away from the supply: the TID expects 12V on a pin called DIS for switching from calendar date to "incoming" String. It is the red/gray wire (same for 8 and 10 letters display). Right now I have connected this pin directly to VCC. In my car I would connect it to ... I dont know how that wire is called - not the positive pole from the battery but the one from the dynamo. Or should this be managed from the Arduino, too?