Just noticed using the ATT USB charger with the same specs as the Nokia charger that my phones touch screen is unresponsive or very very lagging. As soon as I disconnect the phone is fine.
I found that my tmobile micro-usb I used with my lumia also made the screen laggy. It was hard to swipe. Once I put a screen protector on my lumia, the phone was much more responsive. The Lumia Charger thou is the one I use 100% of the time now.
Defective charger maybe? Exchange it, test new one in the store before leaving. That would be my recommendation, provided it wasn't a charger you already had that is.
Touchscreens are *very* sensitive to electrical noise... such as that put out by cheap or improperly spec'd chargers. So a different charger would definitely be on the list of things to try.
Can anyone correlate an unresponsive screen with whether or not the charger cord has a ferrite core (EMI suppressor) on it? Those cores specifically block, or at least reduce, the kind of interference that bothers touchscreen circuits.