If used side by side as per this design, it is noisy. It is ideal that the two boxes be about 12" apart or at least on separate rack shelves. It really has to do with proximity and orientation of the power transformer to the inputs and step-ups.
Cost-wise, there is really not that much difference. The cost of two boxes and umbilical, umbilical connectors, two face plates, etc., has cost too. The one box design would have a bit more sophisticated aesthetics probably, because i would want it to match the SWL 9.0 Ann Ed in the same family, and this costs money too.
The other way to go, to keep it a two box design and also keep the form factor of the phono stage 1/2 width as it is: Make the external supply a 'brick' type small enclosure, that contained the power transformer and power choke only. It could then be tucked away anywhere, away from the phono box. It would not be a 'display' piece, and would not have an AL face plate. It would likely be a black steel, powder-coated box with no switches. Just a power IEC input and umbilical out.
The phono stage could then be very similar in size to what is shown in the photo. In fact, if that were done, the total enclosure cost would be a bit less and this could either drive the cost down a bit, or allow for better quality parts in the phono stage itself.
I see two things here from the feedback. Outboard supplies are desirable because they keep things quiet! They are inconvenient if they take up another shelf space. However, if the umbilical were say 6ft. long and the supply could be on the floor and off the rack, then it may be more attractive.
If that were the case, would it also be attractive for the phono enclosure to be 1/2 size, in case you want to put it beside your TT on a wide shelf, use the MM input with exotic high end Step Up transformers, etc.
All things being equal, is it more appealing for the phono stage to be full width, or more compact?
Thanks,
Dan