The Cisco 30cm Stack Power Cable connects multiple 3750X series switches in order to share power between them.

Switches with StackPower Technology allow for power supplies to be stacked as a shared and common resource.

By using this StackPower cable, you can connect switches with the StackPower technologies.

This is different from the StackWise-480 cables.

The StackPower can be deployed in either power sharing mode or redundancy mode.

What's also great about this technology is its feature of zero-footprint redundancy, basically where you can add one additional power supply to any switch in the stack and that power supply will provide redundancy to the entire stack.

You can also assign priorities to switches and ports for higher availability during outages.

As long as the total available power is more than the power in use in the stack, the StackPower technology will use the excess power for redundancy.