I think there was also a Dr Bott (or some such) converter box that also used the Cube power supply. I discovered this when my Cube ps died and I thought I'd need to buy a replacement (subsequently managed to fix it).

I have asked the same question, as it is odd that a ps capable of running a whole computer and screen had to be used. I have idly wondered if they were manufactured in large numbers and became cheap because surplus to requirement after the Cube tanked. But that is hard to fathom. Presumably the answer is that there is something in the screen or the graphics slot that communicates with the ps, and so part of the whole ADC specification, so that this particular ps was cheaper to use than setting about to engineer a new one.