Does anybody know the power-ratings of that 3rd (2.5 mm / 1/10") socket you see on many airline's arm-rest headphone sockets (KLM, CX and others have 'em)

I was able to determine from searching the 'net that it is the power socket for the NR/NC headsets, and that the tip=Power+ and sleeve=Power-, but no actual powerratings...

TIA!