hp 6710 touchpad + universal charger = crazy mouse movement

So this is a strange one. I've just finished re-imaging some old HP 6710b's for student use in one of our classrooms and noticed this issue. When it is on charger (universal 150W at 19.5v) and disconnected from a network cable, the touchpad just goes nuts! It will randomly click and jumps in a more or less vertical line all over the screen. You don't even need to attempt to move the mouse, just touching the touchpad will cause this. However reconnecting the network cable corrects the problem or replacing the universal charger with an HP charger does as well. Unfortunately, we aren't able to return the universals and spend the extra on the HP AC adapters. Any idea on a fix for this?

side note: careful testing Power Tech Plus universal laptop power supplies. I was checking voltage with the 19.5v tip on it and it sparked and actually shot the inner needle at me. but before that, it looked like it was giving a 20.3v instead of the 19.5v it states. might be the issue.

sounds about right, the universal one vary hugly in quality. if their voltageoutput is wrong you can return them as faulty for a refund.