Why not, just feed the uc +5 regulated from a 7805, off any "generic 12v power supply or wallwart"? This is how I am powering my Picaxe chips during development...
From what I had 'understood' in the past, a voltage regulator needs a few more volts in, that the desired volts out.
I am still new to electronics, so forgive me in advance if I am incorrect, but you cannot get a fixed 12v voltage regulator
such as the 7812 to output a proper 12v from a 12v input, it needs to be 14v or more...
Andrew