You Do Need power plug adapter while traveling from China to Thailand.

Here is Why You Need An Adapter

The outlet and plug type used in Thailand are A, B, C and O and in China are A, C and I. This is how they look like.

China

In China, outlets of type A, C and I are in use.

Type A

Type C

Type I

Thailand

In Thailand, outlets of type A, B, C and O are in use.

Type A

Type B

Type C

Type O