using System.Globalization;
public static void Main()
AddDecimal(-268000m, 12);
private static void AddDecimal(decimal value, int width, char paddingChar = ' ')
var valueAsString = value.ToString(CultureInfo.InvariantCulture);
int length = valueAsString.Length > width ? width : valueAsString.Length;
var field = valueAsString.Substring(0, length).PadLeft(width, paddingChar);
Console.WriteLine(field);