def METHOD_NAME(self):
    """
    Retrieves the serial number of the PSU
    Returns:
        string: Serial number of PSU
    """
    try: val = open(self.eeprom, "rb").read()[0xc4:0xd9]
    except Exception:
        val = None
    if val != "NA" and len(val) == 23:
        return val[-3:]
    else:
        return "NA"