Lavolta BPS305 (PS305D) bench power supply wiring question

[neo2001]

I got this power supply unit a few days ago, did a short test (seems to be ok) and then - of course - opened it up to check it out. After finding a few more or less issues and "imperfections" (like a broken solder pad, bad solder joints, bad/no earthing of the case etc.) I ended up taking it apart completely.

Here are some pictures: https://imgur.com/a/t8QIG

I also attached the schematics which I found here on the board. Unfortunately the display PCB seems to be of a different origin.

There is no problem putting it back together like it was before, but there is one thing about that I do not understand, but would really like to:

On the attached image, on the left side you see the PCB for the output terminals going to the front side of the unit. On the right side is the display board containing the display drivers. This board seems to be getting its own power from the transformer (white/black lines in the upper right). There are also some diodes, a voltage regulator etc..

Back on the left side there are the larger wires coming from the OUT+ and OUT- from the main PCB (blue and black). And there are two pairs of smaller wires which are also connected to OUT+ and OUT- respectively. One pair goes to the display board and the smallest ones go back to the main PCB (plug in CN102).

Now what I don't get is, why they are both connected in reverse? OUT+ is connected to V-, OUT- connected to V+. Also the small wires going back to the main board seem to be connected "wrong" (in the schematic it says "from OUT+", but actually its the OUT- line its coming from and vice versa). Only the main OUT+/OUT- lines are actually connected to the positive/negative output terminals like it's also marked on the PCB.

I'm pretty sure there is a reason for that (no smoke or explosions while testing it), but I would like to know/understand why they could have done it this way? I know that voltage is always a difference between two potentials, so maybe it is enough to just get the "difference" - still it feels wrong to connect it this way.

Also: What is the purpose of the wires going back to the main PCB? Some kind of feedback loop? Any ideas? If you like, you can see much more details on the other pictures I put a link to, above.