So, to use Powerless under the new rules, I would simply declare "all powers" cannot be used until my next turn?

Abilities, however, can no longer be touched, correct?

I seem to recall a ruling that "all powers" meant that, even if you clicked your dial and gained new powers, those powers would also be Outwitted. Is that still so?

Finally, this would also shut down any powers provided by relics, equipment and so forth, right?

Yup, correct on all points.