Why 5V external power? Most ATX PSU are designed to deliver most of their power on the 12V rail(s).
That was the first thing that I thought when I saw those pictures. Sure 5V to ~1V will be a little more efficient, but that's just unloading the problem onto the end user who as to come up with a source of 30A of 5V.It must be a mistake.
Yeah ultimately it is 120VAC/240VAC in and ~1VDC out. The individual steps (or number of steps) doesn't really matter. What matters is the overall efficiency from the wall to the chip. ATX PSU are very efficient at what they do. It is unlikely any design (from wall to chip) will be more efficient than using a 12V rail on ATX PSU. I had even looked into dedicated 12V PSU (i.e ones used for industrial equipment not PCs) and while they are sometimes cheaper they aren't as efficient (efficiency tends to be high 80%).
Making the user try to find a PSU capable of up to 200 amps on 5V (Jupiter pulls 1000W) is going to immediately kill of the most accessible, best priced, and high efficiency options ... ATX (computer) PSU.
Like you said, lets hope it is a typo (it really uses 12V not 5V at board level) and not a horribly stupid design choice.
