After I installed El-Cap Outlook was unable to verify my account password. I thought it's just OS X problem. Now I updated iOS to 9.1 and all my iPhone and iPad also having this issue.
Doh. Today I went to outlook.com and it forced me to change password. Once I did that, the new password works on my iPhone and iPad (both iOS 9.1). That's the good news. The bad news is it still won't work on El-Cap.