The voltage in most Casa Particulares in Cuba is 110V, but you may find that they have a secret outlet, connected to an air-con machine somewhere in the house which is 220V.
Don't ask me how this works, I don't even understand it myself, but one time I had trouble charging an i-pod, it wouldn't charge in the socket in the bedroom, where I have charged countless numbers of mobile phones or cameras. How can this be? Just when you think you know how things work in Cuba, something comes along to test you.
I took it to my family, and Gustavo unplugged the air-con unit in the bedroom and stuck the i-pod charger in it, and hey, it worked! Off course he tried to explain about voltages and the reason it wouldn't work in the other sockets in the house, but I had to admit, I couldn't get my head round it. I was just happy it worked.
I've always been the kind of person that has tried to work things out on my own, refusing to ask for help. But if there is one thing I have learned during my travels, especially in Cuba, if you don't know, ask, it's definitely the best policy.
In any case, coming from the UK or Central America, I usually take both a 2 pin flat head and a 2 pin round head adaptor and that usually works for most chargers that are coming from the UK. I take both as you never know, but mostly I have used the 2 pin flat head adaptor in most Casas in Cuba.
Check out this information on Tripadvisor, but remember it mostly refers to hotel rooms and not Casa Particulares.