Why do you want to reduce the wattage?? If the device that you are hooking up is 24 volts, and only draws 70 watts then there is no problem, it will work. The output of your power supply is 24 volts at 240 watts, only means that you can not draw more then 240 watts from that power supply. It does not mean that it puts out a steady 240 watts. Its the same as plugging something into a wall socket. You have 1800 watts at the plug. 120 volts times 15 amps. So when you plug in a TV that draws 300 watts, thats all you get. As you plug more things into the outlet you draw more wattage. When you exceed 1800 watts, the breaker trips. Do you understand now??