All power adapters provided with XO laptops (or XO-1.5/1.75) are rated for operation at between 90 and 240 VAC, at line frequencies of 50 or 60 Hz. They are electrically compatible with AC power anywhere in the world.
A number of different adapters have been built, as the physical plug design varies from country to country. Newer adapters use a brick design w. a standard unpolarized C8 input, allowing for quick adaptation to local conditions without retooling the power adapter or using an adapter.
This is a photo of the adapter showing the physical plug which would be required to allow charging the XO in Great Britain and other countries.