Passive US (United States Type) Power Converter

Introductions:
Sometimes you just need something very basic and simple to get the thing done. For example, when travel to a foreign country, you need power adapter for different Style of power plug. Yes you can have one that universal and you don't need to check before you do. However, you can go simpler and lighter! just need to know the style of the foreign country and pick up one, then you can go without worries.