The sentence is from Dragon ball, Mutenrôshi, the teacher of Gokû and Krilin, is telling someone about how good his pupils became. He then says this :
I believe てつだって means something along the lines of "in addition", therefore I believe the second part of the sentence means :
In addition to his natural strength, he is hiding an incredible power.
Am i right so far?
Regarding というか, I found that it means something like "in other words", "or rather"... the idea behind being rephrasing what has been said in another/a better/a more accurate manner. Doesn't seem to fit here though...
Thanks for your time.