Many tourists purchase a universal adapter before leaving their home country, but is it really necessary? Also, I want to caution you about an important electrical issue. The answer to the first question is usually, not really. Although I have blown a random kitchen appliance, you do not need to spend a lot of money or even bring an adapter from home unless you have a unique product. In that case, you should contact the manufacturer to make sure.
Even the outlets at the guest houses will be able to work for your mobile phone, small water heater for coffee/tea or your computer, no problem.
One thing I will caution you about is regarding Chinese made electrical products. I had two electric cords attached to my rechargeable lamps to catch on fire. It may take an extra effort, but it's usually wiser to find something from India, or at the very least, get something 'branded' from China.
As a side note, I had a funny experience with a rechargeable lamp. When I saw it on the street corner of a vendor I was so excited that I didn't care about the price. This was shortly after I had arrived in Nepal and was probably missing my own culture a bit. It was a familiar, American brand, Eveready.
I took it home to use during the long winter nights of blackouts of 2011 and about a week later I was just looking at it and something didn't seem quite right about it. I started laughing at myself so hard as I read the brand again-Everday.