Without For loop:
Dim newColumn As New Data.DataColumn("Foo", GetType(System.String))
newColumn.DefaultValue = "Your DropDownList value"
table.Columns.Add(newColumn)
C#:
System.Data.DataColumn newColumn = new System.Data.DataColumn("Foo", typeof(System.String));
newColumn.DefaultValue = "Your DropDownList value";
table.Columns.Add(newColumn);