The principal module is designed to help with identity resolution, both in single-domain and multi-forest scenarios. It can return the resolved identity in a variety of formats.
UserPrincipalName to ADObject
Resolve-Principal -Name tom@contoso.com -OutputType ADObjectNT Account to SID
Resolve-Principal -Name fabrikam\max -OutputType SIDSID To User Principal Name
Resolve-Principal -Name S-1-5-21-584015949-955715703-1113067636-1105 -OutputType UPN