C# ขอคำแนะนำในการ Set Encoding จาก Ascii เป็น UTF8 ด้วยครับ

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using Npgsql;


namespace SecondProject
{
    public partial class Form1 : Form
    {

        private DataSet ds = new DataSet();
        private DataTable dt = new DataTable();
        public Form1()
        {
            InitializeComponent();
        }
     

        private void llOpenConnAndSelect_LinkClicked_1(object sender, LinkLabelLinkClickedEventArgs e)
        {
            try
            {
                string connstring = String.Format("Server=localhost;Port=5432;" +
                   "User Id=tong;Password=1234;Database=dbtes;");
                   
                
                NpgsqlConnection conn = new NpgsqlConnection(connstring);
                conn.Open();
               
                string sql = "SELECT * FROM bank";
                 NpgsqlDataAdapter da = new NpgsqlDataAdapter(sql, conn);
                ds.Reset();
                da.Fill(ds);
                dt = ds.Tables[0];
                dataGridView1.DataSource = dt;
                conn.Close();
            }
            catch (Exception msg)
            {
                MessageBox.Show(msg.ToString());
                throw;
            }
        }
    }
}