Good news and bad news.
I did some more troubleshooting and realised that I had overlooked a potential point of failure: The microSD to SD adaptor. I swapped it out with another I had lying around and it worked! Booted up nicely. I am very relieved. Having said that it still means that I have a faulty power adaptor and a now fried MicroSD to SD card adaptor however I am not too fussed about the latter. I am, for the moment at least, using a switchmode desktop supply. It is bulky but gives me fine grained control over the output.
In response to your question, I tested the power adaptor with a multimeter across the + and - of the USB output.I used an old USB through adaptor with a piggy-backed barrel plug to make it easier to take the following photos.http://flic.kr/p/dvCB8rhttp://flic.kr/p/dvCBfR
I would be quite happy to post the faulty adaptor to you should you wish to investigate it further.