Help requested Power cord Dreamstation

I have a Dreamstation Auto CPAP BLX500S15.
For my holiday on a boat I bought a Powerstation that gives 12VDC because there will be no AC power.
I have an extra original Philips Power Supply PSU (AC powered, with 12 VDC out), where I used the special plug from to be used on my Powestation.
The cable has 3 wires:
Black - ground
Red - 12 VDC
Blue - no idea.

I measured 1,13 VDC during normal operation between ground and blue with the original Power Supply.
In another thread I read to put a 46k resistor between red and blue. I've cut the blue wire, instaaled 46k to red wire and so, used still the original PSU. After boot, CPAP gives 'Check PSU'.
With 46K, I measured 0,5 VDC on blue.
Changed resistor to 22k, and measured 1,0 V but still same message.
What to do with the blue wire to get rid of the error message?