Uninteruptible Power Suply. Used in the Server and PC worId.
It’s a battery that you plug into the wall and the computer/server into it.
It’s purpose is that if there are power cuts, you have time to save your work. Also, it works as a overcurrent/undercurrent protection.
Regarding audio, theoretically, a battery should provide the “cleanest” sound, so, I do not understand why people keep buying power conditioners and power plants when a simple UPS could be cheaper and provide the same functionality, or even more.
Are you sure that your phone interference is not due to the radio signal of the phone?
When does the noise show up? when you get close to your equipment? when you plug it in to charge?