I found the monograph. It's a patent application. It discusses a plethora of signalling used on power management for Respiratory treatment Apparatus.
That link seems to need a key.
It's the 6th result when I googled:
"3.9 resistor pin 3 60 watt power supply resmed"
This paragraph caught my eye:
" For example, if the pull-up resistor represents the
type of power supply, a detection of 3.9 K ohms may be
interpreted by a master controller that the power supply is an
infinite supply (mains). A detection of 2.7K ohms may be
interpreted as a 90 Watt power supply. A detection of 1.8K
ohms may be interpreted as a 60 Watt power supply. A detec
tion of 1.0K ohms may be interpreted as a 30 Watt power
supply. Other voltage levels and coding schemes may also be
utilized to code information about the power supply unit in
this analog manner. Optionally, digital messaging may also
be utilized to detect information about the power supply unit
or other components of the bus. In such a case, a data message
with information from circuits or memory of the power sup
ply unit or based on signals from the detectors or sensors of
the power supply unit may be sent from a processor of the
power supply unit to a system level controller or processor."