When the system is plugged in the mouse pointer keeps shaking. It makes it really difficult to click on any desired icon. When the device is not charging the touchpad works fine.
I am currently using Ubuntu 17.10. I also had the same problem while using Ubuntu 17.04.
This is a hardware problem (maybe is possible to mitigate via software), particularly on Dells. The touchpad doesn't have an stable ground (0 V) level. You can of course try a live distro to confirm.
Workaround: A way I found helps in all cases is to touch with your other hand the ground, some way to touch a metal part of your laptop. One easy way to do this is to plug an ordinary USB to microUSB adapter and touch the metal shield.
Another way is to use a cable or a paper clip (shaped like a 9) around the AC plug.
Sometimes changing the AC power adapter helps.
Of course to avoid all this you can just use an external mouse.
