UPDATE TEST.dba_users u SET
  u.PASSWORD = (SELECT p.PASSWORD
                FROM production.dba_users p
                WHERE p.username = u.username
               )
  WHERE EXISTS (SELECT NULL FROM production.dba_users p
                WHERE p.username = u.username
               );

scott@9i > select 'alter user '||username||' identified by values '''||password||''';' from dba_users;

'ALTERUSER'||USERNAME||'IDENTIFIEDBYVALUES'''||PASSWORD||''';'
------------------------------------------------------------------------------------------------
alter user SYS identified by values 'D4C5016086B2DC6A';
alter user SYSTEM identified by values '1C4DEB81D4E4B2B4';
alter user OUTLN identified by values '4A3BA55E08595C81';
alter user DBSNMP identified by values 'E066D214D5421CCC';
alter user SCOTT identified by values 'F894844C34402B67';