I don't understand why anyone would think that capping the maximum power consumption of a computer would somehow make it more efficient.
That's not how efficiency is calculated for any other appliance, so why computers?
Efficiency is about the amount of work that can be accomplished per unit of energy, not the absolute energy usage. Energy star should know this fact; it's their entire purpose.
A modern computer might use 10x the power of a Commodore 64 but it has 10,000,000x the performance, which makes it more efficient.
Since the efficiency argument doesn't make any sense, then somebody must be lobbying against the sale of high performance computers for some other reason.
Controlling the means of production? Does Disney want to stop people from building a home render farm? Is big tech threatened by home servers? Does Activision-Blizzard want to stop developers from starting their own studios?