Question

Why does Encoding.ASCII != ASCIIEncoding.Default in C#?

Answer 1

This is because ASCIIEncoding derives from Encoding, where Default is defined as:

/// <summary>  
/// Gets an encoding for the operating  
/// system's current ANSI code page.  
/// </summary>  
public static System.Text.Encoding Default
{ get; }  

So ASCIIEndcoding.Default actually returns operating system’s default ANSI encoding.