Comment by adrian_b

Yes, a 10% efficiency is very weird if true.

Nowadays such microwave power amplifiers should be made with gallium nitride transistors, which should allow better efficiencies than the ancient amplifiers using LDMOS or travelling-wave tubes, and even those had efficiencies over 50%.

For beamformers, there have been research papers in recent years claiming a great reduction in losses, but presumably the Starlink satellites are still using some mature technology, with greater losses.