Supplemental PC Power Supplies

A second power supply for graphics cards and internal components

Photo of a Corsair Enthusiast TX650 V2 ATX12V EPS12V Power Supply


Supplemental power supplies are a fairly new addition to the PC component market. The main driving force for these devices is the ever-increasing power consumption of PC graphics cards. Some video cards now draw more power than the processor in the system. With some gaming systems running several video cards, some performance desktop systems can potentially draw as much as a full kilowatt. The problem is that most purchased desktop PCs have only 350 to 500W power supplies. That is where a supplemental power supply can help.

What Is a Supplemental Power Supply?

A secondary power supply resides within a desktop computer case to power components by adding additional power capacity to the entire system. They are designed typically to fit into a 5.25-inch drive bay. The incoming power cable then is routed outside of the case through an available card slot on the back on the case of the system. Various component cables then run from the supplemental power supply to your internal PC components.

The most common use for these devices is to power the latest generation of energy-hungry graphics cards. As such, they almost always have PCI-Express graphics 6-pin or 8-pin power connectors. Some also feature 4-pin Molex and Serial ATA power connectors for internal drives.

Due to the limited space of the supplemental power supplies, they tend to be a bit more restricted in their overall maximum power output compared to a standard power supply. Typically, they are rated around 250 to 350 watts of output.

Why Use a Supplemental Power Supply?

When a power-hungry graphics card is installed into a system that either lacks the proper wattage output to support the graphics card or lacks the proper power connectors to actually run the graphics cards, a secondary supply is necessary. They can also be used to provide additional power for internal components such as those looking to use a large number of hard drives.

Of course, it is possible to replace an existing power supply in a system with a newer higher wattage unit, but the process of installing a supplemental power supply is generally easier than that of a primary unit. There are also some desktop computer systems that use proprietary power supply designs that do not allow a general desktop power supply to be installed in its place. That makes a supplemental power supply an excellent choice for expanding the capabilities of a system without completely rebuilding it.

Reasons Not to Use a Supplemental Power Supply

Power supplies are a major generator of heat within computer systems. The various circuits that convert the wall current down the low-voltage lines inside of the system generate heat as a by-product. With a standard power supply, this isn't too much of a problem as they are designed for air flow into and out of the case. Since a supplemental power supply resides inside of the case, it tends to cause a build-up of extra heat inside of the case.

For some systems this won't be a problem if they already have sufficient cooling to handle the extra heat buildup. Other systems will not be able to cope with this extra heat, which could lead to the system shutting down due to heat tolerance or causing potential damage to circuits. In particular, desktop cases that hide the 5.25-inch drive bays behind a door should avoid using supplemental power supplies. The reason is that the cooling is designed to pull air from the front of the drive bay through the power supply which is then exhausted into the case. (It can also flow the other way depending on the design.) The door panel that blocks the front cover of the drive bays will prevent the sufficient flow of air and will be more likely to overheat the system.