Postgres 9.6 | db<>fiddle

SELECT typname, typnamespace::regnamespace, typdefaultbin, typdefault FROM pg_type WHERE typdefaultbin IS NOT NULL OR typdefault IS NOT NULL;

typname	typnamespace	typdefaultbin	typdefault
time_stamp	information_schema	{FUNCEXPR :funcid 1967 :funcresulttype 1184 :funcretset false :funcvariadic false :funcformat 1 :funccollid 0 :inputcollid 0 :args ({COERCEVIAIO :arg {CONST :consttype 25 :consttypmod -1 :constcollid 100 :constlen -1 :constbyval false :constisnull false :location -1 :constvalue 7 [ 28 0 0 0 110 111 119 ]} :resulttype 1184 :resultcollid 0 :coerceformat 2 :location 105} {CONST :consttype 23 :consttypmod -1 :constcollid 0 :constlen 4 :constbyval true :constisnull false :location -1 :constvalue 4 [ 2 0 0 0 0 0 0 0 ]}) :location 105}	('now'::text)::timestamp(2) with time zone
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CREATE DOMAIN text_x AS TEXT DEFAULT 'X'; CREATE TABLE tbl1 ( id int , col_without_default text_x , col_with_default text_x DEFAULT NULL); CREATE TABLE tbl2 ( id int , col_without_default information_schema.time_stamp , col_with_default information_schema.time_stamp DEFAULT NULL);

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INSERT INTO tbl1(id) VALUES (1) RETURNING *;

id	col_without_default	col_with_default
1	X
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INSERT INTO tbl2(id) VALUES (1) RETURNING *;

id	col_without_default	col_with_default
1	2020-06-02 13:02:58.93+01
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