The words "Online" and "Offline" describe how a UPS delivers power to your load — and that difference decides how well it protects sensitive or critical equipment.
Online (double-conversion) UPS
An Online UPS continuously converts incoming AC to DC and back to AC, so the load always runs on freshly rebuilt, conditioned power. If the mains fails, there is zero transfer time because the inverter was already supplying the load. It also corrects voltage and frequency disturbances continuously. This is the right choice for servers, storage, medical equipment, telecom and industrial control.
Line-interactive UPS
A line-interactive UPS runs the load from mains through an automatic voltage regulator (AVR) that trims high and low voltage, switching to battery within a few milliseconds when power fails. It's a strong, economical middle ground for network equipment and small servers.
Offline (standby) UPS
An Offline or standby UPS passes mains straight through and only switches to battery when the supply fails — a transfer of a few to ~10 milliseconds. It's the lowest-cost option and is fine for desktops, home offices and point-of-sale terminals.
Side-by-side comparison
| Feature | Online | Line-interactive | Offline |
|---|---|---|---|
| Transfer time | 0 ms | 2–4 ms | 4–10 ms |
| Power conditioning | Continuous | Partial (AVR) | None |
| Protects against | All 9 power problems | Sag/surge/outage | Outage mainly |
| Best for | Servers, medical, industrial | Networks, small servers | Desktops, POS |
| Relative cost | Higher | Medium | Lowest |
Which should you buy?
If downtime or a power glitch would cost you data, revenue or safety, choose Online. If you're protecting general office IT, line-interactive is usually enough. For basic desktops, offline is the economical pick. Still unsure? Tell us the load and we'll recommend the right topology.