I once had a client restore a year-old backup on to a test serve, but no one in the organization remembered the password, the password documentation was destroyed and the DBA at that time had long since resigned.
To avoid this problem, I came up with an idea to change a user's password to something I would know, for instance "password of Oracle" or "welcome," via the application and copying the ENCRYPTED_FOUNDATION_PASSWORD for that user to the sysadmin password. Then I ran across the script below on MetaLink, which I think you will find useful.
update FND_USER set ENCRYPTED_FOUNDATION_PASSWORD =' 2DF3E509EB6A33F9607959C0976E25D997166FAB694ACDDAE466414791A44411', ENCRYPTED_USER_PASSWORD=' D2FCA9810D86BCA9BE944D3E2E7A4A9E6CDF89AAD633179B701774083F907C13' where user_name='SYSADMIN';
This was first published in April 2004