Tom's Hardware: "When expanding or upgrading your PC, ensure that your power supply is capable of providing sufficient current to power all the system’s internal devices. One way to see whether your system is capable of expansion is to calculate the levels of power consumption by the various system components in your system, and then compare that to the rating on the power supply to see if it is up to the job. This calculation can also help you decide whether you must upgrade the power supply to a more capable unit. Unfortunately, these calculations can be difficult to make accurately because many manufacturers do not publish detailed power consumption data for their products. In some cases, you can find the specs from a similar component and go by that data instead. Usually components of the same basic design, capability, and vintage have relatively the same power consumption characteristics."