The problem with doing that is that not only would it not save any money, it would probably cost many people a whole lot more. A hub if loaded up can pull a lot of power and the components needed to poperly regulate and filter the AC coming from a landscape tansformer would be expensive and require a redesign of the board which is also not free. Then to add to the injury, large landscape transformers are every bit as expensive as ATX supplies so no real cost savings there either.