So here is some information which should help you. A WATT is an electrical term for power, and power is the time rate of doing work. A WATT is not energy, but just how fast you are using energy. A 100 WATT light bulb uses energy twice as fast as a 50 WATT light bulb. This is why it gives more light.
Energy is work x time.
Remember that the key word is time. Work is the consumption of energy. Energy is what you pay for. The amount of energy in a voltage spike is what does the real damage and the amount of energy a protection device can absorb is the real measure of its worth. Energy is watts x time.