The power levels are a bit all over the place on Star Trek to be honest.
Supposedly 7 of 9's arm can withstand 5 million gigawatts of power.
http://memory-alpha.org/wiki/Watt
Here's a list of some examples of power outputs
By Voyager the Federation were routinely building ships that were producing power well into the terrawatt range.
The federation are also relatively weak in comparison the power house races of ST.
It should also be noted that regularly the enterprise channeled extra energy to the shields...
Given this piece of info.
The warp core aboard a Galaxy-class starship generates 12.75 billion gigawatts per second of energy.
You could argue that the enterprise could theoretically channel most of that energy to the shields (keeping some for life support...firing photon torpedoes etc)