I watched these series as a kid on TV in Russia around 2000 year or even earlier.
The two main characters are a boy, who has some watch-like wristband, and an alien, who is a freely levitating head and can shrink himself to fit into the boy's watches. The alien, for some reason, always had to return inside the watches and live there.
Each episode, as I remember, was about this alien helping the boy to overcome some difficulties using alien technologies.
One episode I remember was the other way around: the alien needed the boy's help, so he made the boy enter the watches, whose interior turns out to be a whole universe (though almost empty).
The series themselves certainly weren't Russian, but I didn't know any foreign language at the time, so I can't say what was the original even if I could hear it beneath the translation.
The animation looked 1980-style.
A few years ago I managed to find on the Internet only a short video from the series, which I can't find anymore. Now all my searches only result in "Ben 10", which is not what I'm looking for: the boy wasn't a shapeshifter.