If I'm imagine the problem right, I would fill the dropdownlists at page_load by calling the DropDownList_Init, and then when a saving gets succeded, I would use postback. Like this:

try
{
con.open();
cmd.ExecuteNonQuery();
}
catch
{
MsgBox("Error")
}
finally
{
Response.Redirect(Request.RawUrl);
}