Following WMIC command will give make and model number along with service tag.
C:\>wmic csproduct get vendor,name,identifyingnumber
IdentifyingNumber Name Vendor
ABCDEF1 PowerEdge 2950 Dell Inc.
C:\>wmic csproduct get vendor,name,identifyingnumber
IdentifyingNumber Name Vendor
ABCDEF1 PowerEdge 2950 Dell Inc.