Here is an original Nagra Kudelski ATN power supply later serial number 664363

Works with a number of Nagra recorders and has a 6 pin Kuchell cable and a standard power cable.
Tested on a nagra 3 and works perfectly, in good condition for its age, you can see pictures for more details. At some stage the case has been resprayed hammertone grey.

Dimensions (LxWxH): 15x6x5cm  Weight: 1,1Kg

From the web

Nagra Kudelski ATN power supply COMBINED SYNCHRONIZING TRANSFORMER AND POWER SUPPLY
The auxiliary ATN power unit can be used as a synchronizing transformer when the camera is being driven by a 60 or 50 cycle power supply. The ATN power unit can also be used to provide external power to the Nagra, operating independently of the internal batteries.