we're going to vietnam tomorrow, and they apparently take both american & australian plugs
(i don't remember about cambodia though, it was about 15 years ago that i went there).
we've just bought an international adaptor that should work in any country. it only takes one plug but has 2 usb ports -
We are just back from a similar trip. The sockets varied a bit between hotels - I took a nifty international adaptor from amazon that included European (round pin) and american (flat pin). Some places also took UK 3 pin. We probably used the European adaptor the most!
Most hotels are fitting universal power points to their rooms, if they don't , they will lend you an adapter
Hotels will lend you an adapter if they dont have universal power points. If you are Australian, Kmart and Big W are selling a higher quality adapter now for $6, much better than the local $1 variety. Although ironically the better ones being sold in Australia are made in Vietnam also.