Potestas est in veritate does indeed mean "Power is in truth" or "There is power in truthfulness," etc.
When it comes to the second part, though, both translations given seem wrong to me. I should say I believe the comma is misleading and does not belong there. The most probable meaning of
Quis vero robustior?
is, especially given the context,
Who is stronger than the truth?
In this interpretation, vero is the ablativus comparationis of verum, "the truth." You could also say: Quis robustior quam verum?
It cannot mean "He who has the truth is stronger," because, well, that's just not what the Latin says. Cui verum, is robustior might work. Google's translation is closer; apparently the algorithm "decided" to translate vero as an adversative particle, "but/however." This is defensible in principle (although in a direct question I would rather expect autem), but makes little sense in context.
Note: veritas can mean "truth" as a concept, or it can mean "truthfulness." Verum, on the other hand, literally "the true," i.e., that which is true, means "truth" in a concrete sense.