Ok, I got the new voltage converter for the cab and it works fine now
I had to pay a real premium for it by going to maplins and getting the best one they had(as that's all they had in stock) but at least I know the candy is ok and it was just a knackered voltage converter.
The one I got is this one:
It was pricey, a lot more expensive than even the website(even allowing for the currency conversion).
But at least it makes absolutely no sound at all thanks to the toroidal construction, no buzzing or humming which is really cool and it has a spare plug socket should I get a US or Jap Xbox 360 or anything else.
It's also 500W compared to the 300W one I got with the cab.
Here's a couple of quick pics of it next to the old one.
Its a lot smaller and fits inside the candy in the corner really nicely.
This thing feels really solid and well built by the way, very industrial feeling to it.
And so it should I guess for the price I paid