You Do Need power plug adapter while traveling from Laos to Sri Lanka.

Here is Why You Need An Adapter

The outlet and plug type used in Sri Lanka is G and in Laos are A, B, C, E and F. This is how they look like.

Laos

In Laos, outlets of type A, B, C, E and F are in use.

Type A

Type B

Type C

Type E

Type F

Sri Lanka

In Sri Lanka, outlets of type G are in use.

Type G