I bought an Inspire USB Power adapter to charge my new iPod Touch by my bedside and when I travel. While I have had no problems with it fully charging my iPod, the other night when I was browsing the web when while I was charging my iPod, scrolling through web pages was very jerky. When I tried to select something it would just jerk out of the way. I had really crushed my iPod screen eariler that day when it was in my pocket and I thought: “great less then two weeks old and I already broke it!”
So I tested a few other apps, and noticed that some had problems and some didn’t. Most noticeably, I couldn’t even play iSolitaire. Grabbing and moving the cards was impossible. Then I thought that maybe charing the iPod while using it was the problem. So, I unplugged the cable and the touchscreen responded normally again.
The problem hit me. The 5V from the cheap USB adapter had to be noisy. The adapter is so light and cheap there can’t be much for voltage regulation, especially under a load like charging the battery. Since the touch screen is a very sensitive, it must be vulnerable to small voltage fluctuations. I tested my theory by plugging the iPod into a USB hub to charge it and found the touch screen operated normally. I don’t currently had an o-scope to test my theory that the 5V regulation is crappy on the Inspire adapter, but I’d wager I’m right.
The moral of the story is if you start to see erratic touch screen behavior when you’re plugged-in — don’t freak — it’ll probably work fine when you unplug it. You may want to get a better adapter or try a different USB port –it’s not worth the risk of damaging you device.