Voltage & Current..

Well, there might be a way to deal with the problem. Most of the poor regulation is down to the following. Most small DC wall warts consist of a transformer feeding a bridge rectifier with a moderate electrolytic capacitor across it. Under low or zero load, the capacitor charges to the peak voltage. As you apply more and more load, you get more and more ripple, and the average voltage goes down (in fact, because there is resistance between the transformer and capacitor, so does the peak). However, you could analyse the ripple and work out what the input was doing. At moderate loads, the capacitor will charge rapidly to something near the peak voltage on each half-cycle, and discharge relatively slowly; at high loads, you'll get a more symmetric ripple. If you want to know in detail, you could sample it, but my guess is if you're just looking for brownouts all you'd need to do is compare the amount of ripple to the average voltage and apply some rule of thumb. Or compare the slope of the rise to the slope of the fall. Of course when the ripple goes away completely you've got no mains input at all :-)