In most plays I've studied, e.g. Erin Brockovich, the end of the second Act II is the "darkest moment" for the protagonist. It's the time when one (at least yours truly) asks, "Why did the hero come in for this? Wouldn't life have been better off without the situation?"
In my favorite plays from childhood, the hero has a "bird in hand" at the end of Act II, and the question is whether or not s/he will get the "big prize." In "My Fair Lady," Eliza Doolittle has learned to be a lady at the end of Act II, and the remaining question is whether she will find happiness with Professor Higgins, or Freddy Eynsford-Hill. In "the Sound of Music," the von Trapp family has gotten Maria as a (step) "mother" by the end of Act II, and the question is whether they can escape the Nazis.
Is there a special name for this kind of plot structure (or the kinds of plays that use it), and is it viewed differently than the other kind of plot structure outlined in the first paragraph? For instance, is romantic comedy more likely to have the second, rather than the first Second Act Structure?