2 or multiple Worksheet_Change different Error Handling / Excel VBA

Question

I am trying to have 2 Worksheet_Change Events on one worksheet that are being triggered seperatly.

For example if I write in "C3" a Number a vlookup is either giving back a name or jumping to OnError GoTo NoSupplier, if i write in "C9" an other vlookup is either giving back a name or jumping to On Error GoTo NoCOMS.

Private Sub Worksheet_Change(ByVal Target As Range)

Dim suppname As String
Dim COMS As String

If Target.Address(0, 0) = "C3" Then
    If Target <> "" Then
        On Error GoTo NoSupp
        suppname = Application.VLookup(Target.Value, Workbooks("Articlepassport.xlsm") _
        .Sheets("Suppliernames").Range("A2:B1000"), 2, False)
        Range("C5") = suppname
    Else
        Range("C5") = ""
    End If
Exit Sub

NoSupp: Range("C5") = "Supplier Data not maintained!"
End If

If Target.Address(0, 0) = "C9" Then
    If Target <> "" Then
        On Error GoTo NoCOMS
        COMS = Application.VLookup(Target.Value, Workbooks("Articlepassport.xlsm") _
        .Sheets("Tabelle2").Range("A2:B11000"), 2, False)
        Range("C11") = COMS
    Else
        Range("C11") = ""
    End If
Exit Sub

NoCOMS: Range("C11") = "COMS does not exist!"
End If
End Sub

Answer 1

You need to add Application.EnableEvents = False so the Sub won't be triggerred multiple times. Before leaving the Sub, you need to restore the settings to the original value with Application.EnableEvents = True.

Note: I've removed your orginal Error Handlers, and I've added a way to deal with the VLookup errors, by adding If IsError(suppname) Then and If IsError(COMS) Then.

Code

Private Sub Worksheet_Change(ByVal Target As Range)

Dim suppname As Variant
Dim COMS As Variant

Application.EnableEvents = False
If Not Intersect(Range("C3"), Target) Is Nothing Then
    If Target.Value <> "" Then

        suppname = Application.VLookup(Target.Value, Workbooks("Articlepassport.xlsm") _
        .Sheets("SupplierNames").Range("B2:H1000"), 4, False)
        If IsError(suppname) Then
            Range("C5").Value = "Supplier Data not maintained!"
        Else
            Range("C5").Value = suppname
        End If
    Else
       Range("C5") = ""
    End If
End If

If Not Intersect(Range("C9"), Target) Is Nothing Then
    If Target.Value <> "" Then

        COMS = Application.VLookup(Target.Value, Workbooks("Articlepassport.xlsm") _
        .Sheets("Tabelle2").Range("A2:B11000"), 2, False)
        If IsError(COMS) Then
            Range("C11").Value = "COMS does not exist!"
        Else
            Range("C11").Value = ""
        End If
    Else
        Range("C11").Value = ""
    End If
End If
Application.EnableEvents = True ' reset settings when leaving this Sub

End Sub