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

Here is Why You Need An Adapter

The outlet and plug type used in Cayman Islands are A and B and in Sri Lanka is G. This is how they look like.

Sri Lanka

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

Type G

Cayman Islands

In Cayman Islands, outlets of type A and B are in use.

Type A

Type B