MarkT:
The lesson here is that a wall-wart is unlikely to be suitable for powering digital electronics unless
used with a proper voltage regulator, or unless it is already "fully voltage regulated" internally - the
good news is that mains USB wall warts are required to be fully regulated to 5V - this is what you
should have gone for I think.
And a very important lesson it was. And i am glad I learned it now and not after making a real project. 