Hmmm... A bit tricky to explain in layman's terms, but I'll give it a crack.
Power is determined by 2 things, voltage and current. To get power, you take the voltage and multiply it by the current. If either one is increased, you get more raw power output.
Think of voltage as pressure, and current as flow. Consider hooking up a garden hose and a fire hose to a water supply with 100 pounds of water pressure behind it. Each hose has the same 100 pounds of water pressure at the nozzle. (This is the water equivalent of voltage). When you let the water flow, MUCH more will come out of the fire hose than will out of the garden hose in any given time period. The amount of water that comes out of the hose is the water equivalent of current. OK... so what's the big deal? Well, with a garden hose, you get a stream of water about 1/2" in diameter. With the fire hose, the stream is at least 6 times the diameter of the garden hose. Would you rather get hit in the chest with 50 pounds, or 300 pounds? If that water were electricity, and your chest were your speakers - you'd want the 300.
The instantaneous part is obvious, it can supply a lot of power, and it can supply it NOW.
I hope that helps.
