If your machine isn't properly grounded, it can build up a static charge and react this way. The third prong on your adaptor's wall cord bleeds off this charge. It can't happen when running off battery.

If that third hole in your outlet isn't properly grounded, nothing plugged into will be. In apartments, particularly ones that have been sold a couple times or have inexperienced managers, the grounding system can become compromised. In any building with basement remodeling or kids running around in the basement, this can happen too.

This is why I suggest trying a different building. It's free to you, and tells a lot right away.