Enforce constraint name uniqueness
will return two IDENTICAL rows with no ability to differentiate which one corresponds to which table/key.


Then don't use information_schema:

select nsp.nspname as constraint_schema,
       c.conname as constraint_name,  
       format('%I.%I', ts.nspname, t.relname) as target_table,
       pg_get_constraintdef(c.oid) as constraint_definition
from pg_class t 
  join pg_constraint c on t.oid = c.conrelid   
  join pg_namespace nsp on t.relnamespace = nsp.oid 
  join pg_namespace ts on t.relnamespace = ts.oid
where c.contype in ('f') 
 and c.conname = 'fk_fooid';


Example: http://rextester.com/DAR30737