Older PR03X

I have just purchased a new latitude e6440 and plugged into the existing docking station setup I was using with my old e6420 (which I'm writing this on): PR03X (T308D A03) (6.7A-10.8A)

It worked in that there was 3 monitor support I basically upgraded for BUT it wasn’t using the mains power through the PSU/ dock but the battery.

I tried swapping in a higher output PSU: PA4E (6.7A / 130 watts) with a PA5M10 (7.7A / 150watts) but it made no difference - the battery was still discharging.

I’m concluding that either my setup is very power hungry and I need an even more powerful PSU or they have been subtle changes to the docking station / e series combo and I need a later version of PR03X or similar? I suspect the latter.

Please confirm and if the dock is the issue the exact model numbers of PR03X/ other docks that will work?