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A client asked: Do I need a surge protector? If the power goes out sometime, what happens w/ the computer?

A surge protector is very important for protecting computers and other electronic equipment from damaging electrical spikes and surges. Fortunately this client already had one. Read the rest of the comments I wrote to her explaining the difference and dispelling the confusion surrounding surge protection and uninterruptible power supplies:

Perhaps you were thinking of an uninterruptible power supply (”UPS”, not to be confused with the brown trucks, of course). There are essentially two types of UPSes. One keeps a battery charged, and if it detects that the power goes out, then it switches over to the battery. It usually takes a few milliseconds to switch over. That may sound very fast to a human, but when computers operate in the millisecond (or faster) range, it can seem like quite a while. The second type of UPS has an Automatic Voltage Regulator (AVR) that charges a battery to continually run the computer. When the power goes out, the battery stops charging, but the equipment never feels a disruption. Your computer receives a continuous supply of pristine electricity. Naturally the second type costs a bit more.

UPSes are rated in VA’s (volt-amps) and Joules. Basically with VA’s, the bigger the number the longer your equipment will run during a power outage. Joules are more commonly touted with surge protectors, but they apply to UPSes, too. Again, the bigger the number, the better the protection against spikes and surges—even nearby lightning strikes in high-end ones.

One thing you generally don’t want to do is plug a surge protector into a UPS—at least into a low-end UPS. A normal electrical current cycles smoothly like an ocean wave from high to low and back again. Output from low-end UPSes (even ones with AVRs) usually produce electrical currents shaped more like square speed bumps. Square waves do not hurt your electronics, but they can cause problems if you plug a surge protector into a square-wave output UPS.

To summarize:

1. [The client has] a pretty darn good surge protector, so [the client is] protected from spikes and surges.
2. [The client is] not protected from sags and brown-outs (minor and major dips in the power), and certainly [the client is] not protected from power failures.
3. Bad power (especially spikes and full-power failures) cause the majority of computer data corruption. Data being written to a disk as the power spikes can be garbled. Drives writing to a disk during an outage, though rare, can write gibberish across the surface of the disk as they spin down (it happened to a computer I used to work on).
4. A UPS of any type will help protect you from complete power outages. UPSes with AVR will also effectively filter out sags and brownouts because the computer is always running on the battery. Non-AVR UPSes kick in when power drops below a certain point (some brown-outs are enough; some aren’t), and there’s always a slight delay, so you ever so slightly risk some data loss (it really depends on how sensitive your particular computer is to low-voltage situations—some are touchy; some don’t seem to notice).
5. It is okay to plug a UPS into a surge protector, but you should never plug a surge protector into a UPS unless the UPS produces pure sine-wave output (which consumer-grade UPSes will not).
6. Only critical devices (computer and monitor in [the client’s] case; possibly the printer) should be plugged into the battery powered part of the UPS. Other peripherals (notably speakers, laser printers, and anything non-critical) should be plugged into the non-battery protected part of the UPS or a regular surge protector. That way, you might lose your audio (speakers powered off), but you have maximum run-time for safely shutting down your computer and monitor.
7. Paying a little more for a UPS which can communicate to your PC and tell it to shut down if the power goes out can be very helpful if you aren’t home when the power goes out.