is this a US made product designed for the UK market?
It's the P.S.U. for a 3Com/U.S. Robotics external modem, about 8 or 9 years old. This appears to be a specific international version of the modem different from the North American version -- Only has CE etc. approval marks not UL/CSA/FCC, documentation and onboard help systems don't include American/Canadian options, and so on. Says Made in Hungary on the sticker.
The P.S.U. is the one specifically for the U.K., Irish Republic, Malta, etc. No clue as to its country of manufacture.
How hard was it to open the case?
Not hard at all after I put a large screwdriver between the sections and just snapped the threads out!
Yes, it was screwed together, but with screws having a peculiar head for which I had no tools. Why can't they just use regularly slotted or Philips on something like this?