function checkPass($username, $password){

 # Get current domain using logged-on user's credentials
 $CurrentDomain = "LDAP://" + ([ADSI]"").distinguishedName
 $domain = New-Object System.DirectoryServices.DirectoryEntry($CurrentDomain,$UserName,$Password)

if ($domain.name -eq $null)
{
 write-host "---- $($username): Authentication failed - please verify your username and password."
 # exit #terminate the script.
}
else
{
 write-host "+++++ $($username): Successfully authenticated with domain $($domain.name)"
}

}

get-spmanagedaccount | % { $_.UserName } | % { checkPass $_ xxxx }