Connected the PRTG IPMI sensor to 4x Supermicro IPMI nodes with default ADMIN/ADMIN password no probs.
Then after changing each password the IPMI sensor in PRTG wouldn't take the new password properly. Of course, I confirmed that I could login to each node with the new password.
Even removing/re-adding the IPMI sensors didn't help. It just kept giving error 221 for wrong username/password.
Then when creating a new testuser in the IPMI with that same new password, the IPMI sensor was able to login fine.
So to me, it seems like the IPMI sensor is wrongly caching the password until the username changes.