The fact that this only happens when on AC power is a bit concerning. I’d call Dell and get a replacement.
The problem is likely related to the controller for charging the battery. You could test this theory by unplugging the battery while it’s plugged in and see if you still have the problem.
The other thing it could be related to is the inverter that runs your backlight. Most laptops will brighten the screen when on AC power. If this is the case, you have a potentially very dangerous situation on your hands. This is probably unlikely though, since you would likely be getting strong shocks no matter what.
In any case, call Dell and get a replacement. Also, don’t use two hands at once on your track pad.
It sounds like your laptop has issues with a ground, since the voltage on the laptop chassis is floating high. You should not have gotten an electric shock. If possible, open the laptop, and try to see if any components are electrically shorted to the laptop chassis and/or other connectors.
If you only experience the shock when the charger is connected to the laptop, then you should stop using the charger immediately and get a new one. Check the charger itself for ground faults. If you are using an ungrounded charger, there may be an electrical fault in the actual socket. Start with the charger, and work from there.
Again, there is no voltage in the laptop which is high enough to shock you. I have not seen any laptop chargers provide a DC output higher then 20 V. Look into the charger or any short circuits (either in the laptop or charger), but again, since you’re getting shocked, ensure that your charger is not the problem.
A simple test to figure out if it is your laptop or your electrical wiring, you can connect another device, e.g. a printer or a monitor – which has a three pin plug to the laptop (usb port or video out port) and if the current/vibrations/shocks are gone, it is your wiring. Because the three pin device is providing the ground.
You would do well to use a tester, or get a proper electrician to run this test for you. If it is your wiring, it is still a question whether it is your internal wiring fault or the electricity companies fault. You should first call your electricity company to get them to check that they are providing the ground/earth for you correctly. If that does not solve your problem, then unfortunately it is your internal wiring which is faulty. This could be expensive. Or you could just keep the three pin device connected and ignore the problem.
just wrap the middle cord with plastic cover in the charger and use it. i also had this problem after doing it’s working fine(no shocks)