|Surges||These are brief (and sometimes catastrophic) increases in the voltage source (very high voltage for a very short time). They can originate with the power source (the local power company), but most often are due to lightning strikes.|
|Spikes||Spikes are very short overvoltage conditions. Spikes are measured in nanoseconds, while a surge is measured in milliseconds.|
|Sags||These are brief decreases of voltage at the power source.|
|Brownouts||If a sag lasts longer than one second, it is called a brownout. The overloading of a primary power source can cause brownouts. Some brownouts are "scheduled" by power companies to prevent overloading of circuits and potential catastrophic failure of the system.|
|Blackout||This is a complete power failure, which can be caused by equipment failure (local or regional) or accidental cutting of power cables. When the power returns after a blackout, there is a power spike and danger of a power surge.|
The most easily recognized problem is a complete failure of the power supply. This is easy to detect because in the event of a failure, the computer will not begin to boot up (no lights, no sound). If there is apparently no power, be sure to check the power source and the plug at both ends: the outlet and the computer.
If you are experiencing intermittent failures such as memory loss, memory corruption, or unexplained system crashes, don't rule out the power supply. It is often the culprit. Fortunately, it is easy to check and replace.
Good power supplies have line-conditioning circuits, but these might not be sufficient enough in locations where the power source has substantial quality flaws. If you have problems with several systems, or if a second power supply still does not fix a related complaint, add a UPS with good line-conditioning features.