Laptop touchpad works incorrectly when on power supply

My initial feeling is that the new power supply is causing electrical interference. The touchpad is likely connected internally via USB, which can (won't always of course) be susceptible to interference.

Here's a test for this.... do you see the incorrect behaviour if you have your new power supply plugged in and sitting next to your computer, but not actually plugged into the machine?

I have the same problem (erratic or no control on the touchpad) and found it disappeared as soon as I unplugged the replacement (and probably not from the laptop manufacturer) power supply from my HP laptop. I then found this post on another forum that seems pretty accurate:

My guess is that there might actually be something wrong with the touchpad circuitry, or you have a power supply problem as suggested in this clip from Wikipedia:

If the computer is powered by an external power supply (PSU), the detailed construction of the PSU will influence the virtual ground effect; a touchpad may work properly with one PSU but be jerky or malfunction with another (this does not imply any electrical risk whatsoever, a delicate capacitative ground, not a contact ground, is at issue). This has been known to cause touchpad problems when a manufacturer's PSU, which will have been designed to work with the touchpad, is replaced by a different type. This effect can be checked by touching a metallic part of the computer with the other hand and seeing if operation is restored. In some cases touching the (insulated) power supply with some part of the body, or using the computer on the lap instead of on a desk, while working can restore correct operation.

I can confirm that my issue disappears when I do the following: - unplug the power supply from the laptop. - touch a metallic part of the laptop (i.e. USB port) - place the laptop on my lap (probably earthing it as above). - touch the power supply with my hand.

All in all it seems to be down to the electronic circuitry of the replacement (non-manufacturers) power supply is not the same as the manufacturer's original unit.

So I either have to use it on my lap or plug a USM mouse in if using on a desk.

I had this issue just now, then found this while attempting to troubleshoot. At first I thought this was caused by a recent Ubuntu update that conflicted somehow with my Dell Mini 10.

Turns out it was the power outlet I was plugging my laptop into. What's even more odd is when the power strip I have the power adapter plugged into is switched off, the mouse still does not work. So I started plugging in the switched off power strip with my power adapter and laptop plugged into it to other outlets and with all of them my mouse works except this one outlet. So I then discovered that although everything else I've plugged into this outlet seems to work, when the fish tank light which is plugged into this same outlet is on, the mouse on this laptop doesn't work whether the power strip is switched on or off. Just last week though, this very plug/power configuration was working perfectly. Maybe this 1 year old netbook is starting to show it's age? At any rate, I hope this helps someone!