Connecting the Negative (Ground) on two PSUs - wire size & fuses ?

[plasmadrive]

I have run two power supplies in parallel and it did work but I did see some gliching. This was just a day or two of testing but when it is easy to power inject correctly, I see no reason to make this part of your permanent setup. Besides I did see so issues with effects especially in fading.

In true parallel? V+ to V+ and V- to V-? Or did you just connect the V- together?

If your supplies are not made for true parallel then I would expect issues without some special care.