I suggest downloading the generic Naim Power Supplies manual and looking at all the connection diagrams for an understanding.
Short answer is they provide different voltages and number of voltage rails so any one power supply works with a subset of Naim products. One size cannot fit all but often one supply can work with two or three different products.
Indeed there are variations (It is Naim after all ) In those cases it’s powering the analogue stages in the CD players rather than taking over the whole supply. For the Naits, it’s powering the pre-amp stages.
The writing has been on the wall for the existing power supplies for some time now, as Naim could not realistically release updated models without giving them a low power consumption standby mode. The 555PS is still officially called the CD555PS despite being sold exclusively for streamers since the CD player was discontinued.
The new NPX300 of course conforms by using a similar standby mode to the current streamer and Uniti range.
Not sure I’d use the term ‘thwarted’. New products have to comply with EU regulations on electricity consumption in standby mode. The old models were developed when energy prices were low, and decimatimg the environment was not on anybody’s agenda. Times change.