My laptop adapter is ungrounded, and because of that, I feel slight vibrations when I stroke the laptop surface (if I unplug my laptop, the vibrations go away, so it can't be the fan). The adapter is double-insulated so it should be perfectly safe without grounding - but those vibrations are still worrying me. It might be electricity that's passed to me, but I'm not sure what it really is. What are those vibrations, and are they harmful for me or my laptop?
It is neither dangerous nor harmful.
Note that I am assuming that you are using a good-quality mains adapter, preferably from the laptop manufacturer. The reason a good-quality adapter costs more is that more care is taken in designing and making it, and better parts are used to make it.
What you are feeling is caused by a very small, not physically harmful, amount of leakage current through a small capacitor between the primary and secondary windings of the transformer in the power adapter.
However, if it is unbearably unpleasant, you could get a Class I mains adapter (that is a Roman numeral I, as in II, IV, etc.), which connects the output ground to the mains ground. With one of those, you must power it from a grounded outlet.
Or you could place your laptop on an earthed surface, but you may well not have a convenient one.
More information: Earthing: Is it important for laptops
I did some more research about it, and found this blog from Dell explaining what happens: http://en.community.dell.com/dell-blogs/direct2dell/b/direct2dell/archive/2007/04/24/8522
TL;DR: it's not harmful to the user and the computer
“Tingle” Sensation Explained
For those of you who really want a better understanding of what the reported “tingle” sensation is, we have worked with our electrical engineers and safety teams to share a detailed description of what exactly is going on. Here are some things that about the “tingle” sensation that Mike posted earlier that I think bear repeating:
- It is not harmful to you the user.
- It is not harmful to any of the system’s internal components.
- This issue is not specific to Dell.
- This issue is not specific to notebook computers even. A “tingle” sensation may be felt on many electronic devices that use a 2-prong AC power source under specific environmental conditions.
So, what’s this “tingle” sensation and what causes it? The “tingle” sensation is the transfer of energy from you, a 2-wire AC adapter/ system ground and contact with an earth ground. A “tingle” sensation may be felt when touching the exposed metal portions of the notebook and/or 2 -prong AC adapter when the AC adapter is plugged in. The “tingle” sensation is not an indication of a failed or defective ground. To generate the “tingle” sensation, you must be earth grounded at the same time you are touching an exposed metal piece of the notebook while the notebook is plugged into the 2-prong AC adapter. The voltage will always be there when the notebook is plugged into the 2-prong adapter, but it is harmless to you as a user and the notebook itself. In fact, in the vast majority of cases, the voltage is not noticeable to you at all. Certain environmental elements can increase the chances of experiencing the "tingle sensation" such as weather and humidity or a person's skin condition (oily, dry, etc.) There's a bit more on this at the Dell Sweden support site.
The source of the “tingle” sensation is not your notebook, it's the 2-prong adapter. This “tingle” sensation is not caused by any defect in Dell's 2-prong adapters—they work as they are designed. Other notebook manufacturers ship with 2-prong adapters as well, and users of those notebooks may experience a “tingle” sensation if conditions are right. 2-prong adapters are becoming more common these days because they smaller, lighter and more convenient to carry—all things which are important to many notebook customers.