Why is is that all my outdoor power cords have 3 prong polarized plug recepticles and all the outdoor equipment such as blowers, weedwackers, etc have 2 prong nonpolarized plugs? How do I safely connect the one to the other? Also why aren't the cords marked with the proper wattage?

Hi,
Well your cables may be required to have those plugs even if not used. Generally equipment will use a nonpolarized plug if it makes no differences where the power and neutral are.
You will have to take the wattage on the equipment and divide by 120V to get the current requirement in amps. Generally 18ga is 10A, 14ga is 15A, 12ga is 20A and 10ga is 30A. That said it does matter how long the cord is since the voltage will be reduced by resistance and the equipment wants to produce the same power, it will "try" to draw more current.
Peace,
Clarke

2 prong plugs can be poloraized as well. The neutral is wider. Look closer.