Likewise sorry to hear of your problem.
I have also been using a Powerdown adaptor for I can't remember how long "maybe a year or so" without any problems, and as mentioned above I have quite a lot plugged into it.
With the one they returned, have you tried it yet and does it work?
If you have not tried it (which is quite understandable), then try it firstly on something like a table lamp where there would be minimal damage if it's still faulty (which I doubt).
I can only assume that you either had a faulty one, or it went faulty.
Or, just by chance, it was at that particular time that your PSU decided to pack-up taking the graphics card with it.
I know it's of no consolation to you, and I do really feel for your loss, but on the rare occasion I ever have to send anything away, I mark the item/s with a secret marker pen, the like used for post-coding your goods.
***********************
Dave.
Did you consider the BC to ES adaptor for the energy saving lamps?