It's quite possible it uses a simple mechanism like a rubber roller that is constantly spinning, driven by a motor.
The keys would push a lever or arm against the roller, so friction with that provides the power to move the type arm.
If several keys have got pressed at the same time, there could be too much load on the mechanism for the motor to start up.
Leave it powered off and disconnected.
I'd first try lifting each type arm in the type basket all the way to the paper roller and let it drop back. Start at one side and do each in turn all the way across.
Do not force anything, they should be free with just a light spring to pull them back.
If any are stuck part activated, I'd guess that should "reset" them.
Try power again, but disconnect quickly if it only buzzes - if it's left stalled too long it may burn out the motor.
If you can get to the motor you could try gently turning it back & forth slightly to see if that unsticks anything.
There are lots of typewriter enthusiast sites on line with masses of user and service manuals - but I cannot find anything useful for Adler electric models so far...
There may be some other makes that use similar mechanisms though.
typewriterrepairbible.com