Rega IT Replacement Laptop AC Power Adapter/Charger for COMPAQ PRESARIO CQ42-404AU CQ42-404AX CQ42-404TU CQ42-405AU laptop enables you to operate your notebook or charge the Adapter from electrical power outlets. If you are running your computer on AC power with a Adapter installed, the adapter charges the Adapter (if needed) and maintains its charge. When the system is off, the AC adapter will charge the Adapter and then maintain its charge. Made from highest quality parts each Rega IT replacement adapter confirms to specifications similar and guaranteed to meet or exceed your laptop's minimum requirements. Each adapter also passes necessary authentication certifications like CE, ROHS etc. Before leaving the factory, so you can be rest assured for its quality, durability and performance. Please make sure that you are selecting the correct adapter as per you old charger specification. Please compare your old Adapter Power Rating i.e. Volts (V), Amps (A), Watt (W) and Pin / Tip / Connector Size.