Hi Sri,
You can set the value for the Combo box in GGC by assigning DataSource property to the particular column. Please refer the below code snippet which illustrates this.
this.GridGroupingControl1.TableDescriptor.Columns[2].Appearance.AnyRecordFieldCell.CellType = "ComboBox";
StringCollection rows = new StringCollection();
//Points to first index of combo box item. Does nothing even if it got selected.
rows.Add("John"); rows.Add("James"); rows.Add("Christy");
GridGroupingControl1.TableDescriptor.Columns[2].Appearance.AnyRecordFieldCell.DataSource = rows;
Please refer the sample from the below link which illustrates the above:
http://websamples.syncfusion.com/samples/Grid.Web/6.1.0.23/F70197_new/main.htmRegards,
Raji