Online vs Offline UPS: Which One Do You Need for Your PC, Router and CCTV During Load-Shedding?

For a home or office PC, a monitor and a router, an offline UPS is usually all you need. It is affordable, compact and switches to battery quickly enough for normal computers.

An online UPS is designed for equipment that cannot tolerate even a tiny interruption or poor-quality power, such as servers, network racks, medical devices and some industrial machines. It costs more and is mostly used in businesses rather than homes.

For a Wi-Fi router and ONU, a small mini DC UPS is often the neatest choice, because it powers them directly at the voltage they need and can keep your internet running for hours.

In normal operation, an offline UPS passes mains power straight through to your devices while charging its battery. When the mains power fails or drops too low, it quickly switches to the battery and its inverter takes over.

That switch takes a few milliseconds, called the transfer time. Normal PC power supplies can bridge such a short gap, so your computer keeps running. For example, the ZKTeco ZKUPS-900W-LED 1500VA Offline UPS lists a transfer time of 4 to 6 ms, and the Prolink PRO1201SFCU 1200VA Offline UPS lists 2 ms typical.

Strengths and limits

• Strengths: affordable, efficient, quiet and compact.
• Limits: it does not clean up the mains power while it is on mains, and there is a short transfer gap when the power fails.
• Best for: home PCs, office desktops, monitors, small printers and CCTV recorders.

A line-interactive UPS is an improved offline design. It adds automatic voltage regulation (AVR), which can raise or lower the output voltage when the mains voltage sags or rises, without switching to the battery. That saves battery wear when the voltage in your area is unstable but the power has not fully cut.

Many UPS models sold for homes and offices include some form of voltage regulation, and sellers often still call them offline UPS. If your area has frequent low voltage in the evening, look for AVR in the specifications or ask before buying.

An online UPS works differently. It constantly converts the incoming AC power to DC, which charges the battery, and then converts it back to clean AC power through its inverter. Your devices always run from the inverter, never directly from the mains.

Because the inverter is always running, there is no switch when the power fails. The transfer time is effectively zero, and the output stays stable even when the mains voltage and frequency are poor. Online UPS units also produce a pure sine wave output.

Strengths and limits

• Strengths: no transfer gap, the cleanest and most stable power, best protection against voltage problems.
• Limits: costs more, uses more energy, produces more heat and often has a cooling fan running all the time.
• Best for: servers, network racks, banking and office systems that must not go down, medical equipment and sensitive machines.

If you need an online UPS for a server room or a business system, contact the Index IT team with your load details so we can suggest a suitable option.

UPS models are sold by their VA (volt-ampere) rating, but your devices use power in watts. The two are not the same. The watt rating tells you the real load the UPS can support.

Look at these examples, as listed on Index IT:

Ratings as listed on Index IT in October 2026.

In all of these, the watt rating is about 60% of the VA rating. So never assume a 1000VA UPS can run a 1000W load. Always compare your total load in watts with the UPS watt rating.

• Step 1, list your devices: PC, monitor, router, CCTV recorder, and anything else that must stay on.
• Step 2, find each device's power use in watts: check the label on the adapter or device, or the power supply rating of your PC. The PSU rating is the maximum, and a normal office PC uses much less.
• Step 3, add them up and keep headroom: choose a UPS whose watt rating is comfortably above your total, ideally with 20% to 30% to spare.
• Step 4, decide on backup time: a small load on a big UPS lasts longer. If you need more minutes, choose a larger UPS or one with a bigger battery.

Typical sizing examples

A desktop UPS is designed to give you minutes, not hours. Its job is to keep your PC on long enough to save files and shut down, or to bridge a short power cut. For long load-shedding, an IPS or a generator is the right tool for fans and lights, while the UPS protects your electronics.

Backup time depends on the battery size and the load. Manufacturers usually quote it at full and half load. For example, the Power Pac 1200VA Offline UPS lists 30 minutes at full load and 40 minutes at half load, while the Prolink PRO1201SFCU lists up to 15 minutes. Real backup time is shorter as the battery ages.

Ways to get more backup time

• Connect only the devices that really need backup.
• Turn off the monitor and speakers when you only need the PC to finish a task.
• Choose a larger UPS, so the same load is a smaller share of its capacity.
• Replace the battery when backup time drops noticeably.

When the power goes, many people find their PC is fine on its UPS, but the internet drops because the router and ONU switch off. A mini DC UPS solves this. It plugs into the wall and powers your router and ONU directly through DC cables, so there is no inverter and very little energy is wasted.

The XTREME XUP63-8.8 Mini DC UPS lists an 8800mAh lithium-ion battery, a maximum load of 17W and outputs of 5V, 9V and 12V DC, plus PoE 15V and 24V. Before buying any mini UPS, check the voltage on your router and ONU adapters and make sure the UPS provides those outputs.

See more options on the mini UPS page.

A CCTV system that turns off during a power cut stops recording at the worst possible time. The recorder, the camera power supply (for analog systems) or the PoE switch (for IP systems) and the router should all be on backup power.

CCTV loads are usually small, so an offline UPS in the 650VA to 1000VA range can keep a small system running for a useful length of time. Sudden power loss can also damage recordings and stress the hard disk, so a UPS protects your footage as well as your uptime. For more on this, read our IP vs analog CCTV guide and our CCTV storage guide.

• Do not plug in laser printers, heaters, irons or kettles: they draw heavy current and can overload a desktop UPS.
• Keep it ventilated: do not place the UPS inside a closed cabinet or against a wall without airflow.
• Use a proper earthed socket: earthing matters for safety and for surge protection.
• Let it charge: charge a new UPS fully before relying on it.
• Watch the battery: sealed lead-acid batteries wear out over time. When backup time drops sharply or the UPS beeps constantly, the battery likely needs replacing.
• Keep the box and invoice: some brands require them for warranty claims. The Power Guard PG650VA-CS listing, for example, notes that the box is mandatory when claiming.

For most homes and offices in Bangladesh, an offline UPS sized correctly in watts is the right choice for PCs, monitors and CCTV recorders. Add a mini DC UPS for your router and ONU to keep the internet on. Choose an online UPS when you run servers or equipment that must never see a power interruption.

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