SharePoint 2010/2013: Update Farm Credentials
A common task that every SharePoint administrator needs to do is to update the SharePoint Farm credentials when the password changes. They may be able to do this automatically by using the new SharePoint 2010 feature to plan automatic password change.
No command in PowerShell updates the farm account, you have to switch to the tool “STSADM” only.
If it's SharePoint 2010, go to the path C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\Bin folder and type the below STSADM to update.
If it's SharePoint 2013, go to the path C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\Bin folder and type the below STSADM to update:
stsadm –o updatefarmcredentials –userlogin DOMAIN\username –password $password$
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If you find a different solution, please report it as a comment to this post. This will be useful to the SharePoint Community. Be sure to double-verify it: undo your solution and verify that the problem comes back, then redo it and verify that the problem goes away.
Important note:
If you are working on your own development environment that's elevated to Domain Controller, you must be vigilant on "Change Password" notifications by Windows. Before the password expires automatically, you must use the above command and then use the same password to update Windows too. Or else your SharePoint Farm won't work until you manually change the password on all accounts use your password expired credential (usually Administrator).