Overall, I like the sound of this, though there are a couple things I could see as being potential issues that might discourage widespread adoption. One would be that using an A, B, C, D, E type scale brings with it people's view of other things using that scale. In most school systems, an E would be considered a failure, and a D would be close to failure. A company might not want to put a badge on their product that carries with it the connotation that it isn't up to standards.
What the ETA scoring system might imply as being a "near failure", the 80 Plus system might consider as having a "bronze" certification or better. People think of "bronze" as a good thing. In the Olympics, getting a bronze medal means you're the third-best in the world. Everyone on the podium is a "winner", and likewise all certification levels in the 80 Plus program sound like awards, that you would want to have on your box. The same can't be said for all the certifications in the ETA program, despite them being more meaningful. Even though a manufacturer might score an "ETA D" on their product, they might stick with only advertising the "80 Plus Bronze" rating they got from the other certification company, despite the ETA rating technically being "better".
Also, the Lambda ratings are a great addition, and it would be nice to see them used on other products, but I feel the badges look much too similar to those for the ETA ratings, which could lead to some confusion. You can't tell at a glance whether a badge is advertising the product's efficiency, or its sound level. The word "ETA" or "LAMBDA" is only meaningful to someone already familiar with the rating systems, and the tiny power plug or sound wave icon is so small that it's practically unnoticeable. Having a tag like "EFFICIENCY" or "SOUND LEVEL" printed directly below the existing badge design might help to avoid some confusion.
I do think the rating system sounds great though, and providing a URL to a detailed database entry with informative graphs is a nice touch.