Studies have shown that about 80% of all computer problems are caused by bad power. About 80% of all power problems are power sags or brownouts. These drops in voltage can corrupt data as thoroughly as a power surge.
Surge protectors do not protect computers from drops in voltage. At best, surge protectors will attempt to prevent the computer from being damaged by a power surge.
To protect computers from low-power conditions, use an uninterruptible power supply (UPS, or battery backup), with power line conditioning. A UPS has a battery that can run the computer for several minutes if the electricity goes out. In the very least, this provides time to close programs and shut down the computer properly.
Most good UPS devices also act as power line conditioners. A power line conditioner regulates the voltage coming into the computer. It prevents both spikes and drops in voltage.
NOTE: Some inexpensive battery backup devices do not include power line conditioning. In addition, there are power line conditioners that do not include a battery backup. To be safe, always get a device that includes both battery backup and power line conditioning.