I am slightly confused about the wonder (sudden brain block about name, the big dam one) that gives you 'power' in evry city on the continent. I thought this acted like hydro plants in each city that also give you power, the little lightening symbol on the city, but after building it you can still build hydro plants.

After building the wonder does hydro plant give you even more production or what, I know I should know this but am confused

it does give you power to every city on the continent. You are still able to build hydro dams in your cities though because it doesn't provide the damn, only the power. It may be useful to build dams in your cities if your at risk of losing your Three Gorges Dam wonder. Or spend the hammers on an army to defend it.

so just to be certain the built dams/hydro plants add nothing if you build them after three gorges ( I got stuck on Boulder dam and couldn't think passed it).

so just to be certain the built dams/hydro plants add nothing if you build them after three gorges ( I got stuck on Boulder dam and couldn't think passed it).

Yes. You get NO additional benefits.
I believe that having power gives a city 2 :yuck:.
And Coal Plants give an additional 2 :yuck:.