Technically scrambled. Let me try to untangle it.
The "e-bomb" produces, very briefly and in a focused direction, an electromagnetic field equivalent to that of an "isotropic" (i.e., theoretical omnidirectional) radiator operating at about 2 billion watts - the same power as is continually produced by the generators at Hoover Dam.
Uh, I can see why they simplified it <>=<)B^).
This is still scrambled. The sentence seems to be saying that the bomb yields as much ENERGY as Hoover Dam does in 24 hours, and that this figure would be 2 billion watt-seconds (joules). But since I don't know what the power capacity of Hoover Dam is, I can't say if this is actually what is meant.
Remember: Energy is what weapons blow stuff up with -- measured in joules, ergs, watt-seconds, and such things. Power is a measure of how fast something produces the energy.
You could produce 2 billion watt-seconds of energy from a hamster cage, but it would sure take a lot of hamsters!