The selection of the right waterproof DC power cable will depend on voltage/current requirements, environmental conditions, and specifics in installation. It shall be designed according to the requirements of power but must also be durable in the environment if it is exposed to UV rays, water, or very extreme temperatures. The compatibility of connectors with your equipment and safety standards is another thing that you will need to consider. Lastly, consider the scaling up of your setup if it may require more power in the future.