pg_dump 9.2.x command does not work with pg_dump 9.2.3
I'd venture that it has nothing to with pg_dump version but that it may be an invisible spurious character on the command line that is causing this mess. As a demo, if I type this in cmd.exe, it works as expected at first:


  pg_dump -U postgres postgres >out.db


But now if I come back on this command with Arrow-Up, position the caret just before the -U option, add a non-breaking space by hitting Alt+255 on the numeric keypad, and validate this command, it yields the error you mention:


  pg_dump: too many command-line arguments (first is "-U") Try "pg_dump
  --help" for more information.