In SQL Server, the NEWID function generates a UUID value.
In PostgreSQL, you can use the GEN_RANDOM_UUID function.
SQL Server:
-- Generate a new UUID SELECT NEWID(); /* 68C13548-EC51-4A2F-8CA2-9FCB2D1A8DC2 */
PostgreSQL:
-- Generate a new UUID SELECT GEN_RANDOM_UUID(); /* a438a056-5be0-42f7-93d6-262a1ff1b103 */
For more information, see SQL Server to PostgreSQL Migration.