1. How would you use the second set of X values?

2. The code above deletes all series at the beginning of the routine, then adds back as many as it needs. New series added to a chart use default formatting. The new code below applies new data to the existing series, which reuses any customized formatting. If it needs more series, it adds them as needed. At the end, if it needed fewer series than were initially present in the chart, it removes the excess.

Sub PopulateChartFromTable2()
  Dim cht As Chart
  Dim rng As Range
  Dim sPrompt As String
  Dim iSrs As Long
  Dim nSrs As Long
  Dim xSrs As Long
  Dim srs As Series
  Dim iRow As Long
  Dim iRowStart As Long
  Dim iRowEnd As Long
  Dim sSeries As String

  If ActiveChart Is Nothing Then
    MsgBox "Select a chart and try again.", vbExclamation
    GoTo ExitSub
  End If

  sPrompt = "Select a three-column range with your data."
  sPrompt = sPrompt & vbNewLine & "  Column 1: Series title"
  sPrompt = sPrompt & vbNewLine & "  Column 2: X values"
  sPrompt = sPrompt & vbNewLine & "  Column 3: Y values"
  sPrompt = sPrompt & vbNewLine & "Avoid blank cells"

  On Error Resume Next
  Set rng = Application.InputBox(Prompt:=sPrompt, Type:=8)
  On Error GoTo 0
  If rng Is Nothing Then GoTo ExitSub

  Set cht = ActiveChart
  nSrs = cht.SeriesCollection.Count

  sSeries = ""
  iSrs = 0
  For iRow = 1 To rng.Rows.Count + 1
    If rng.Cells(iRow, 1).Value <> sSeries Or iRow > rng.Rows.Count Then
      If iSrs > 0 Then
        iRowEnd = iRow - 1
        If iSrs < = nSrs Then
          Set srs = cht.SeriesCollection(iSrs)
        Else
          Set srs = cht.SeriesCollection.NewSeries
        End If
        With srs
          .Values = rng.Cells(iRowStart, 3).Resize(iRowEnd + 1 - iRowStart)
          .XValues = rng.Cells(iRowStart, 2).Resize(iRowEnd + 1 - iRowStart)
          .Name = rng.Cells(iRowStart, 1).Value
          .ApplyDataLabels ShowSeriesName:=True, _
              ShowCategoryName:=False, ShowValue:=False
        End With
      End If
      iRowStart = iRow
      sSeries = rng.Cells(iRow, 1).Value
      iSrs = iSrs + 1
    End If
  Next

  If nSrs >= iSrs Then
    For xSrs = nSrs To iSrs Step -1
      cht.SeriesCollection(xSrs).Delete
    Next
  End If

ExitSub:
  Application.ScreenUpdating = True
End Sub