The original TED talk is still worth watching. Amy Cuddy is a strong communicator and lessons on public speaking can be learned from that.

As for the efficacy (or not) of the "power pose", it might be worth considering that for some people it may have a psychological placebo effect.

That is to say: Perhaps if a person believes strongly enough that doing a thing will make them more confident, then that person's confidence will be improved by doing that thing.