How much does your line voltage fluctuate? Maybe you don't even need it.
I would think changes in output related to the tube's temperature would be orders of magnitude higher than output changes from the voltage fluctuation typically encountered in a US city.
But I'm just thinking out loud here.
Having said that, I do agree with you that 100w capacity does not seem like enough. But on the other hand, if it is an Aristo stabilizer, what head would they have ever sold that would have such a low power drain? a 35mm head (which I don't think they ever made). So if its not for your light source, what else would that Aristo stabilizer be intended for??
( So, basically I'm saying just what you are saying and not offering any answer to the question.. sorry )