And since I'm the kind of person who hates having loose ends... I took the power supply outside (it's -22C here) and let it get nice and cold, then hit it with a hammer, which basically shattered the shell. So, I can now confirm *visually* that the three ground wires all go to the same place on the power supply and are all soldered together, and the three 19V lines all go to the same (different) place and are also all soldered together. And that as they say, is that. There is, of course, a risk someone will connect it to a power source at more than 19V, or has reversed polarity (not that big a risk these days since positive center pin has become pretty much the standard - but still possible), or is unregulated and so sends spikes. Again, if you have any concerns or doubts, don't do this project.