In the grid, the default values come from GridDataBoundGrid.Model.ColStyles[col].CellValue. So, in your formload, if you have the DataTable.Columns[col].DefaultValue's, you could move them into the ColStyles.
Here is a little sample showing how you might do it. The sample starts with 10 rows, but works ok if you just start with 1 row.
Maybe something like this will work for you.
But if you want to dynamically set the values without relying on the defaults in the DataTable, try handling CurrentCellMoved.
private void gridDataBoundGrid1_CurrentCellMoved(object sender, Syncfusion.Windows.Forms.Grid.GridCurrentCellMovedEventArgs e)
{
GridCurrentCell cc = this.gridDataBoundGrid1.CurrentCell;
if(cc.RowIndex == this.gridDataBoundGrid1.Model.RowCount)
{
this.gridDataBoundGrid1.Binder.BeginEdit();
this.gridDataBoundGrid1[cc.RowIndex , 1].Text = "defaultcol1";
this.gridDataBoundGrid1[cc.RowIndex , 2].Text = "defaultcol2";
}
}