The three types of UPS
Offline or standby UPS units only kick in when the power goes and are the cheapest. Line-interactive units also correct voltage rises and dips without using the battery: they are the usual choice for home and office. Online double-conversion units always power the equipment from the inverter, with the most complete protection, but they cost more, are noisier and use more power.
| Equipment | Typical draw | Suggested UPS | Detail to check |
|---|---|---|---|
| Router and fibre | 15–30 W | 400–600 VA | Hours of runtime |
| Office PC and monitor | 100–200 W | 650 VA | USB port for shutdown |
| Gaming PC and monitor | 350–500 W | 1200–1500 VA | Pure sine wave |
| 2 to 4-bay NAS | 30–60 W | 650–850 VA | USB compatibility with the NAS |
How to read the table
The ranges are a guide: use the UPS calculator with your real power figures, ideally measured with a plug-in meter. What most separates a cheap UPS from a good one is not the VA rating, but the waveform, whether the battery can be replaced and the software to shut equipment down automatically.
VA, watts and runtime
UPS units are marketed in VA, but what matters is the watts they deliver, usually between 60% and 90% of the VA. An 850 VA UPS may deliver only about 480 W. Always check the watt figure on the spec sheet.
Runtime depends on load: the same UPS can last half an hour with a router and three minutes with a gaming PC. Look for the maker runtime chart; at home the realistic goal is time to save and shut down, not to keep working for hours.
Automatic shutdown for NAS and servers
If you connect a NAS, choose a UPS with a compatible USB port. The NAS detects the outage and shuts down cleanly before the battery runs out, avoiding damage to the drives. Synology, QNAP and TrueNAS recognise most USB UPS units; check the compatibility list before buying.
In networks with several machines, the NAS connected by USB can tell the others to shut down too.
Batteries and maintenance
UPS lead-acid batteries last 3 to 5 years, less if the unit sits somewhere warm. Check that they can be replaced without special tools and what a spare costs: sometimes a slightly more expensive model with easy-to-find batteries is the better deal.
Many UPS units run a periodic self-test and warn you when the battery is weak. Do not ignore that warning.
How to work out what you need step by step
List everything you want to protect and note its real power draw: a plug-in meter is the most reliable, and the figure on the label is usually the maximum, not typical use. Add it up, add 25% headroom and divide by the UPS power factor to get the VA.
Then decide how many minutes you need. Five to ten minutes are enough to save your work and shut down; to keep the router and fibre running through long outages, look for models with larger or expandable batteries.
Where to place it
Put it somewhere cool and ventilated, away from radiators and direct sunlight: heat is what shortens battery life the most. Let it charge for a few hours before connecting equipment and set up the shutdown software before you need it, not during the first power cut.
What not to plug into the UPS
Laser printers, heaters, hair dryers and other appliances with heating elements have power peaks that can overload it. Plug only what must keep running into the battery outlets and use the surge-only outlets, if there are any, for everything else.
Frequently asked questions
What is a pure sine wave?
An output identical to the mains supply. Many budget UPS units produce a stepped wave that some active PFC power supplies do not handle well, and the computer may switch off right when the power fails.
Does a UPS protect against lightning?
It helps with moderate surges, but no home UPS guarantees protection against a direct or very close strike. Unplug equipment during heavy storms.
Can I plug a power strip into the UPS?
It is not recommended: it is easy to overload it without noticing and many makers advise against it in their manuals.
Is a UPS with lithium batteries worth it?
LiFePO4 lithium batteries last more years, cope better with heat and weigh less, but the UPS costs quite a bit more. They pay off for critical equipment, in hot network cabinets or when you do not want to replace batteries every few years. For a home PC or router, a lead-acid model is usually enough, and replacement batteries for it are cheap and easy to find.
Sources and method
Network UPS Tools — hardware compatibility list · Methodology