Yes, you can use it in Vietnam. I haven't, but I HAVE used it in China, Hong Kong, Thailand and Australia in the past year, and they are all the same power as Vietnam.
Try reading it with a magnifying glass.
As a general observation, for the past 15 years the technology has existed to economically manufacture power supplies that work on all electrical networks worldwide. Power supplies for all quality electronics take advantage of this technology so manufacturers don't have to make and stock different power supplies for different countries. Thus you will find that virtually all laptop computers, cell phones, iPods, MP3 players, etc. come with these "universal" power supplies. All that has to be changed moving from one power grid to another is the plug or the power cord.
To be safe you should read the label on the power unit to verify that it is not the rare exception. But if it says *100-240 V 50/60 Hz* it is a universal device and can be used anywhere.
This is NOT true for high power devices such as desktop computers, hair dryers and other things with motors, stereo systems, etc.
