"Es una fuente de dinero."
Translation:It is a source of money.
The below seem like inadequate explanations for why. Perhaps it is b/c "He is a source of money" would be an uncommon meaning for the sentence, compared to "It is..." However, in the right context, it seems that it could well mean this, based upon what we have learned, and my understanding of the implied subject in Spanish.
"He is a fountain of money" is a legitimate thing to say in English, if you're trying to say that he is extremely generous or superb at doing things that make a lot of money for himself and others.
On Spanishdict.com, "fuente" is the first definition for the submitted word "fountain".