Redundant power supply
Found more commonly in servers and other high-end computers, a redundant power supply contains two (or more) power supply units inside it. Each power supply is capable of powering the entire computer and only one runs at a time. If one fails, the other power supply starts running to keep the computer powered up. The switch between the power supplies is seamless, so as not to interrupt the normal use of the computer. The picture is an example of what a redundant power supply.
The redundant power supply is important for servers and other highly important computers, to minimize the chance of a complete computer shutdown or failure. The cost associated with the redundant power supply is higher due to the design and functionality, starting at around $300. It is not commonly found in home computers due to this higher cost, but is still available if a consumer is willing to pay the higher price tag.