...and because I repaired it myself when it first died (it was that or wait maybe a month), it’s not covered by warranty.
However, there are some bright & enthusiastic people in Perth (Hi, Mal!) who have an answer sitting on their shelves. I’m eagerly inspecting our snail-mail (hi, Sharon!) as it arrives in expectation of seeing one shortly.
I know that the same peoples’ DC-to-DC converters work well, or at least that one worked flawlessly all of the way across the Nullarbor, in all temperatures & variable humidity (it started raining on us at Eucla and we brought that with us through SA & Vic to Tas), so I’m looking forward to a longer happier life with this one than the manufacturer’s device.
The website doesn’t mention compatibility with TwinHead 15D Notebooks, but it’ll learn soon, I think.