How to implement some super admin feature to facilitate password retrieval for existing users?
You can't. Drupal passwords are hashed, not encrypted, the key difference being hashes are one-way. 

With Drupal 6's non-salted MD5 hashes, a rainbow table might get you there, but with D7's salted SHA512 hashes would be much tougher. The time spent trying to do this would be better spent trying to find an alternative to your need of listing all user/pass.