Efficiency of electrical appliances (and other things, for that matter) uses a scale of A-G, with A being the most efficient. However, the scale has proved to be inadequate - there are now also A+ and A++ efficiency scores.
I wondered where this would end.
A+++ - this fridge generates its own electricity
A++++ - this fridge converts atmospheric CO2 into coal.
A+++++ - DO NOT SWITCH ON! This fridge reverses the expansion of the universe, and thus the arrow of time, preventing you from switching it back off again, ultimately leading to a reverse big bang ....