Bringing European Electronics to the US: Theory and Practice

Theory goes first, as it often happens.

Theory

Electric household appliances, as their name implies, are supposed to do (arguably) valuable job by consuming energy in form of electric power. If I were to design an ideal world, I'd make infrastructure for supplying appliances with power the same in the whole world. By chance or by reason, it is not the same. The most widespread standards for power supply mechanisms are ones that originate from (i) Europe, (ii) UK, and (iii) US.

A relatively straightforward consequence of varying infrastructures is presence of devices that are designed differently in terms of power supply. It's interesting that the more hi-tech a device is, the more standard-independent it is.

Let's get to the meat of a general case. A common appliance is wired to two infrastructure-related requirements:
1) Plug type;
2) Set of input current requirements: voltage (a value or, perhaps, interval) and current frequency (usually, 50 or 60 Hz or [50;60]Hz). 

An example: my electric toothbrush bought in Russia requires 220-240V and 50-60Hz.

We come to the main statement of this section:

To make your appliance work in an infrastructure you have to take care of both requirements above.

Laptops' and mobile phones' chargers usually have a broad range of permissible input voltages and frequencies, so you'll only need to find a plug adapter. However, to use my toothbrush in the US, I have not only to adapt the plug, but also to convert voltage somehow.

What happens if you don't convert voltage and/or frequency? God knows. It might work almost imperceptibly, not work, or burn out. Depends.

Note: I didn't touch the issue of alternating and direct current because I could easily abstract my theory out of it. Grounding options are also of little significance.

Practice

I am retarded enough to bring my desktop (ATX casing) into the US through two flights, both quite intense. It was madness, but I did it!

My traveling desktop.

Shortly after my long-awaited arrival I realized that voltages don't match - 110 vs 220. Such a washout! A decision came fast - a ~$40 voltage converter (below) solved my problem, and now I have a sub-network for European appliances.

The lifesaver of the desktop.

P.S. Carrying desktops around sucks infinitely!