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A feature of many models of modern server-oriented computer hardware, as well as high-end routers and other network hardware. A computer or other device is equipped with two or more power supplies, each of which is capable of supplying the device's entire demand for power. Extra circuitry on board provides for load balancing between the two power sources, and uninterrupted failover in the case that one should quit providing electricity.

Having multiple power supplies has two chief advantages. First, power supplies have been known to fail; having two live sources of power means that a single point of failure in a power supply will not take your server down. Second, you can connect your two power supplies to two different UPS units and power circuits, ensuring that a UPS failure or circuit breaker blowout will not affect your server.

Please note that some high-end servers, especially ones with several disks, have two or more non-redundant power supplies: both must be powered before the server will run. In some cases, the second power supply is necessary only if a certain number of disks, CPUs, or other power-intensive components have been added. Check your documentation before you go hot plugging those transformers.

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