You Do Need power plug adapter while traveling from Belgium to Cambodia.

Here is Why You Need An Adapter

The outlet and plug type used in Cambodia are A, C and G and in Belgium are C and E. This is how they look like.

Belgium

In Belgium, outlets of type C and E are in use.

Type C

Type E

Cambodia

In Cambodia, outlets of type A, C and G are in use.

Type A

Type C

Type G