Next to a back drive, a UPS is the most important accessory you need if you own an iMac, Mac mini or Mac Pro. Essentially a power strip with a battery, a UPS will keep your Mac running if you have a power outage or even a split-second power interruption. Then you can shut down your Mac gracefully and not lose any work. Most UPSes today come with a USB connection that you can connect to your Mac. Then you get a new section in System Preferences where you can set your Mac to shut down on its own if power is out and the battery is in use.