And, of course, the computer stops providing its normal services. Unprotected equipment is fried, and data is lost. A surge is like a spike, but it's less extreme and lasts longer. Causes are similar to those of spikes, but surges can also be caused when high voltage devices are turned off. They can also destroy equipment, or they can simply stress it unduly.
Noisy power can cause erratic device behavior.
A good UPS can deal with all of these problems and provide steady power to your Linux box. On the surface, a UPS seems to be a pretty platform independent device. That sort of approach works if you're only interested in surviving short power outages. And that's why it's awfully helpful if your UPS vendor is Linux-friendly. There are free utilities for monitoring UPS devices, too.