NewTek 3Play 3PXD820 has redundant, replaceable power supply units. When you i) disconnect or ii) power down just one of the modules, or iii), if a PSU should fail, a beep is sounded to alert you. If you wish, you can mute the alert by pressing the green button on the back of the unit.
Q: Where can I obtain replacement or spare Power Supply modules?
A: Contact NewTek Sales for purchase information for spare components.