Just to give proper closure to the thread I started... Here are some pictures of my current setup, including the box I put together to distribute power to the mount and camera cooler and supply 5v to the Raspberry Pi from a common 12v input.
As I commented earlier, I'm now using a Meanwell 12V 12.5A power supply. I fitted it with a long cable ending in a 5.5 x 2.1mm plug. I know there are better connectors, but in this way I can still use it directly into the mount if necessary (without modifying the mount). I also feel I rather see the cable disconnect itself if accidentally pulled.
The box is thus fitted with a female 5.5 x 2.1 mm plug input. It could be alternatively sourced from a 12v battery. Here some views of the inside:
You can see the stripped HP 2x USB cigarette plug supply (sorry for my messy soldering job). There is still room in the wigo connectors to supply for an additional 12v output.
This is the box assembled, the cables for the mount and the camera cooler come directly from the inside (no connector):
And here is the box attached to the moving RA arm of the HEQ5 pro via a velcro strip:
The input cable comes from below. USB supply cable for the Raspberry Pi (which is attached behind the telescope in the first picture) and 12v cable for the camera cooler have a loop to allow for DEC movement and are rooted through an elastic band below the telescope saddle. The 12v for the mount goes around the RA arm to the mount input (as seen in second picture). The box remains permanently attached to the mount.
I'm extremely happy with the results, and still amazed at how much a good power supply can improve things.