"Your rage has unbalanced you..."

Usually, the dark side seems to grant extra -or quicker- power (see Anakin, Luke, Rey, Ezra, Koth, Cere, Vos...). So what are your thoughts as to why it apparently didn't work for Obi-Wan on the Turtle Tanker?

It's a shortcut. Sometimes using a shortcut bites you in the ass.

Obi-wan didn't connect with it enough. Shadows of the empire, Jedi Quest, and Darth Bane all say that if you don't connect wholly to the darkside as a Jedi, then you will actually be hindered because your powers will be in rapport fighting one another. Granted that's the legends explanation but the same should hold true for the darkside. In the marvel Vader run he notes the Inquisitors would be weak since they were former jedi and had not connected wholly to the darkside, this is why he tortured and isolated them each and why they are all such animalistic monsters. In fact Ninth sister comments on this in fallen order when she talks about how the loss of limbs is nothing compared to the "conditioning" she had already recieved.

This thread is now for quoting my post and changing the ending. Go.

Anger doesn't always empower Jedi, unfocused anger can blind Jedi and cause tunnel vision, the anger itself needs to be focused to be used effectively. Maul was using Dun Moch in that instance to mentally unbalance Obi-Wan for his own sadistic enjoyment, and we know that Dun Moch can disrupt the victim's connection to the Force, which is what happened to Obi-Wan there. Moreover, using anger and hatred most effectively requires one to be a trained in the Dark Side of the Force, Obi-Wan obviously hasn't done that because he's a Jedi who tries his best to follow the Jedi Code that rejects emotions, and he would've been kicked out of the order for attempting to learn the ways of the Dark Side. He did have anger issues in his padawan years though, he was so impatient and brash that he nearly got kicked out of the order IIRC, but as of TCW, Obi-Wan no longer retains these anger issues because he's a different guy at this point in time. He did experience a brush of the Dark Side in his previous encounter with Maul because he witnessed Maul murder his surrogate father Qui-Gon, but Maul didn't use Dun Moch to mentally unbalance Obi-Wan in that encounter anyway, not to mention that was a one off. Obi-Wan as a quintessential Jedi master, is untrained in the Dark Side of the Force.

Obi-Wan didn't harness the dark side. He basically let anger cloud his judgement and rushed forwards doing a stupid manoeuvre.

@Latham2000 See, the way I understand it, taunts are employed to shift the focus of the opponent to trying to control their emotions, not so much to make them actually give in to the dark side. Luke, Ezra and the others (except maybe Anakin and Vos) weren't trained in the dark side, yet they received significant boosts whenever they became angry. You must be at least partially right though, since Obi-Wan is the less impulsive character on the list. Perhaps I'll need to take a look at those Legends quotes @> Korriban mentioned in order to gain a better understanding on the subject.