I'm guessing the mini adapters for the Mk2a were simply well made and lived up to the specs, then. Others who've bought power supplies with 1a @ 12v ratings from Radio Shack have reported that they occasionally cut out.

Basically, my reluctance to recommend the power supply from the top of this thread is based on the fact that it's got a Radio Shack logo on it. That practically guarantees questionable quality...