For the HSK, what do I need to know about characters which appear differently?
The Chinese characters are used not only in Chinese but also several other languages (such as Japanese). The written form of the same character may differ in these languages. And on a computer, these differences are usually controlled by fonts (as they use the same code point).

The second form in your original post is a Japanese version of 喝, which will be considered wrong if used in Chinese. You might be using a font designed for Japanese to display the character. Try change to a font that is designed for displaying Chinese (like SimSun), you will get the correct Chinese written form.