This 430 Watt silent power supply from ATXPowerSupplies.com is UL Listed. You will not find them any quieter than this; a pindrop can be heard next to this power supply! Internal relay inside the power supply is actuated by the power switch connected to your motherboard. This power supply also has an external switch. As you can see by the connectors on this power supply it fully supports P4 and AMD CPUs. This is currently out of stock, we will send out the upgrade option of LPZ18 500 Watt Power Supply, if this model is bought.