On 3 of the 7 Eris's I've activated on my number, the touch screen would go haywire even plugged into the HTC wall charger.
Some of the cheaper wall chargers aren't made as well, and the method use to transform voltage to the correct (5v) amount, although the same, is hindered by cheaper materials and workmanship.
The touch screen on our phone is known to go haywire when high-power chargers are connected, as the positive and negative terminals of the battery are VERY close to the capacitive sensitivity range of the touchscreen.
A capacitive touch screen works by the fact that your finger (or whatever you use) has an electromagnetic field.
The 'charging' action of your phone generates (obviously) an electromagnetic field. Our phones are designed so compact that where the battery terminals connect to the charger (behind the bottom part of your touch screen), the minor electromagnetic field created actually creates a 'touch' on your touchscreen. Once the touch starts 'touching', your capactive touchscreen keeps seeing it.
It has been reported a THOUSAND times in different threads of people saying "My Eris has gone crazy!" or "Ghosts in my phone!" and things like that. It's that some phones, by manufacturing deviation (VERY slightly) are more prone to it than others - and some chargers (like the cheap one I use) render the touchscreen almost USEless with most Eris's, and especially the sensitive ones.
It is to note that, even those seeing the problem severely (like my first Eris) virtually NEVER see it when plugged into a computer to charge (charges at 1/2 or 1/3 speed, sometimes just called a 'trickle charge') because the electromagnetic field generated is much smaller.