Generate password and shuffle the characters

In a recent project I had to create a function to generate a password with an exact number alpha characters, numeric and symbols and then shuffle them.

numOfNumericChars (Indicates number of numeric characters);

numOfAlphaChars (Indicates number of alpha characters);

numOfSynbolChars ( Indicates number of symbol characters)

validNumChars (Valid characters for numeric. Default is all characters from 0- 9)

validAlphaChars (Valid characters for alpha. Default is all characters from a- z  and A-Z)

validSymbolChars (Valid character for symbols. Default is all characters in  !-+_@&$#%)

C#

public string generatePassword(int numOfNumericChars, int numOfAlphaChars, int numOfSynbolChars, string validNumChars = "1234567890", string validAlphaChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ", string validSymbolChars = "!-+_@&$#%")  
     {  
       StringBuilder res = new StringBuilder();  
       Random rnd = new Random();  
       while (0 < numOfNumericChars--)  
       {  
         res.Append(validNumChars[rnd.Next(validNumChars.Length)]);  
       }  
       while (0 < numOfAlphaChars--)  
       {  
         res.Append(validAlphaChars[rnd.Next(validAlphaChars.Length)]);  
       }  
       while (0 < numOfSynbolChars--)  
       {  
         res.Append(validSymbolChars[rnd.Next(validSymbolChars.Length)]);  
       }  
       string stgPassword = res.ToString();  
       //Shuffle password  
       char[] array = stgPassword.ToCharArray();  
       Random rng = new Random();  
       int n = array.Length;  
       while (n > 1)  
       {  
         n--;  
         int k = rng.Next(n + 1);  
         var value = array[k];  
         array[k] = array[n];  
         array[n] = value;  
       }  
       return stgPassword = new string(array);  
     }