c# sha512 salt

using RandomNumberGenerator;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;
 
namespace HashingAlgos
{
    public class PasswordWithSaltHasher
    {
        public HashWithSaltResult HashWithSalt(string password, int saltLength, HashAlgorithm hashAlgo)
        {
            RNG rng = new RNG();
            byte[] saltBytes = rng.GenerateRandomCryptographicBytes(saltLength);
            byte[] passwordAsBytes = Encoding.UTF8.GetBytes(password);
            List<byte> passwordWithSaltBytes = new List<byte>();
            passwordWithSaltBytes.AddRange(passwordAsBytes);
            passwordWithSaltBytes.AddRange(saltBytes);
            byte[] digestBytes = hashAlgo.ComputeHash(passwordWithSaltBytes.ToArray());
            return new HashWithSaltResult(Convert.ToBase64String(saltBytes), Convert.ToBase64String(digestBytes));
        }
    }
}

static byte[] GenerateSaltedHash(byte[] plainText, byte[] salt)
{
  HashAlgorithm algorithm = new SHA256Managed();

  byte[] plainTextWithSaltBytes = 
    new byte[plainText.Length + salt.Length];

  for (int i = 0; i < plainText.Length; i++)
  {
    plainTextWithSaltBytes[i] = plainText[i];
  }
  for (int i = 0; i < salt.Length; i++)
  {
    plainTextWithSaltBytes[plainText.Length + i] = salt[i];
  }

  return algorithm.ComputeHash(plainTextWithSaltBytes);            
}