A short power interruption can shut down a server, interrupt network connectivity or corrupt data stored on a NAS. An uninterruptible power supply (UPS) helps organizations reduce this risk.

This guide explains how a UPS works, which technical criteria matter and how four models available through Amazon compare. It is written for small and medium-sized organizations looking to protect servers, network equipment, workstations or storage systems.

What is an uninterruptible power supply?

A UPS is an electrical device positioned between the mains supply and the equipment that needs protection. It contains a battery and automatically supplies temporary power when the normal electricity supply fails.

Depending on the model, a UPS can also compensate for voltage fluctuations and protect connected equipment against power surges. Its two primary purposes are to keep equipment operating during a short interruption and to provide enough time for systems to shut down safely during a longer outage.

A UPS should not be confused with a generator. Most office UPS systems only provide power for several minutes under a significant load.

How a UPS supports ISO 27001

A UPS can support the implementation of ISO/IEC 27001:2022 Annex A Control 7.11, Supporting Utilities. Purchasing a UPS does not, however, automatically implement the control.

The organization should determine which systems require continuous power, their expected electrical load, the required runtime, whether automatic shutdown is necessary, who maintains and tests the UPS, and how test results are documented. Selection should be based on availability requirements and the organization’s risk assessment.

The most important UPS selection criteria

1. Real power in watts

The watt rating describes the maximum real load a UPS can support. This is normally more useful than the VA rating when comparing products. A UPS rated at 1,200 VA may, for example, only support a maximum load of 750 watts.

The normal load should remain comfortably below the stated maximum. As a practical planning value, operating at approximately 60–70% of the watt rating leaves capacity for load variations and future equipment.

2. Battery runtime

Runtime depends on the connected load. A unit that runs for ten minutes at half load may only run for two or three minutes at full load. Calculate the combined consumption of all protected devices and consult the manufacturer’s runtime curve.

3. UPS topology

• Offline or standby: The least expensive option, suitable for individual workstations and relatively stable power conditions.
• Line-interactive: Includes automatic voltage regulation and can correct certain voltage fluctuations without using the battery.
• Online double-conversion: Continuously supplies the load through the UPS electronics. It offers the greatest isolation but normally costs more and consumes more energy.

Line-interactive models are generally the most practical category for small servers, NAS systems and network equipment.

4. Output waveform

Some less expensive UPS devices produce a stepped approximation of a sine wave while operating on battery. A pure sine-wave output is preferable for sensitive equipment and devices with active power factor correction (PFC), although it usually increases the purchase price.

5. Automatic voltage regulation

Automatic voltage regulation (AVR) corrects certain under-voltage and over-voltage conditions without switching to the battery. This can reduce unnecessary battery use.

6. Shutdown and monitoring

A USB connection and compatible management software allow a computer, server or NAS to monitor the UPS and initiate a controlled shutdown. This is important when an outage may last longer than the available runtime.

7. Replaceable battery

UPS batteries are consumable components. Their lifetime depends on temperature, use, charging cycles and battery quality. A replaceable battery can extend the useful life of the UPS and reduce total cost of ownership.

Comparison methodology

The scores are editorial assessments based on published manufacturer specifications. They are not the results of an independent laboratory test.

UPS comparison at a glance

Availability on Amazon can change. Confirm the exact model number, socket type and seller before purchasing.

APC Back-UPS BX750MI-GR: the compact entry-level choice

The APC BX750MI-GR is a compact line-interactive UPS rated at 750 VA and 410 watts. Its four Schuko outlets are protected by both the battery and surge protection. AVR helps compensate for certain voltage fluctuations without immediately switching to battery operation. The battery output uses a stepped approximation of a sine wave.

Manufacturer data for this platform indicates approximately eight and a half minutes of runtime at half load and around one minute close to full load. Actual runtime varies with load, battery age and environmental conditions.

Strengths

• Compact and comparatively accessible
• Line-interactive topology with AVR
• Four battery-backed Schuko outlets
• Sufficient for low-power network equipment or a small NAS

Limitations

• Relatively low maximum wattage
• No LCD
• Stepped rather than pure sine-wave output
• Limited headroom for growing configurations

Best use case: A router, firewall, network switch and small NAS with a combined load well below 300 watts.

Editorial score: 67/100

Find the APC BX750MI-GR on Amazon.de
Manufacturer information

APC Back-UPS BE850G2-GR: best for workstations and home offices

The APC BE850G2-GR is rated at 850 VA and 520 watts. It has eight Schuko outlets, although not every outlet is backed by the battery; the remaining outlets provide surge protection only. Its flat design is convenient under a desk or when mounted on a wall. USB-A and USB-C charging connections are included, and the internal battery is user-replaceable.

This is an offline UPS rather than a line-interactive model. It is therefore most appropriate for individual workstations and relatively stable power environments.

Strengths

• Eight Schuko outlets
• 520-watt capacity
• Replaceable battery
• USB-A and USB-C charging ports
• Space-saving form factor

Limitations

• Offline topology
• Not every outlet receives battery power
• Stepped output rather than a pure sine wave
• Less suitable for demanding servers

Best use case: A workstation, monitor and selected network equipment in a small office or home-office environment.

Editorial score: 72/100

Find the APC BE850G2-GR on Amazon.de
Manufacturer information

Eaton Ellipse PRO 1200 DIN: the balanced business option

The Eaton Ellipse PRO 1200 DIN provides 1,200 VA and 750 watts of capacity. It uses line-interactive technology with AVR. The device has eight Schuko outlets: four provide battery backup and surge protection, while four provide surge protection only.

Eaton specifies approximately nine minutes of runtime at half load and two minutes at full load. An LCD provides operational information, and the HID-compatible USB connection supports automatic integration with major operating systems. The battery is replaceable.

Strengths

• Good balance of capacity and runtime
• Line-interactive topology with AVR
• LCD status display
• Replaceable battery
• USB communication for automatic shutdown
• Three-year manufacturer warranty, including the battery

Limitations

• Only four outlets are battery-backed
• No pure sine-wave output
• Larger and heavier than basic office models

Best use case: A NAS, small server, business workstation or combined network configuration requiring monitoring and automatic shutdown.

Editorial score: 85/100

Find the Eaton Ellipse PRO 1200 DIN on Amazon.de
Manufacturer information

CyberPower CP1600EPFCLCD: best overall performance

The CyberPower CP1600EPFCLCD is the most capable model in this comparison. It provides 1,600 VA and 1,000 watts, uses line-interactive technology and generates a pure sine wave while operating on battery.

All six Schuko outlets receive battery backup and surge protection. The manufacturer specifies approximately 9.7 minutes of runtime at half load and 2.6 minutes at full load. The device also includes a colour LCD, AVR, a replaceable battery and management software.

Strengths

• Highest watt capacity in the comparison
• Pure sine-wave output
• Six battery-backed Schuko outlets
• Colour LCD
• Replaceable battery
• USB monitoring and management software
• Suitable for active-PFC power supplies

Limitations

• Higher purchase price
• Relatively heavy
• More capacity than a small router-and-switch configuration requires
• Up to approximately 40 dBA according to the manufacturer

Best use case: Workstations, small servers, NAS systems and network equipment where output quality, compatibility and capacity are more important than minimum cost.

Editorial score: 92/100

Find the CyberPower CP1600EPFCLCD on Amazon.de
Manufacturer information

Which UPS should a small business choose?

• Choose the APC BX750MI-GR for a router, switch or small NAS with a limited load.
• Choose the APC BE850G2-GR for a workstation or home-office configuration where numerous sockets and a space-saving design matter.
• Choose the Eaton Ellipse PRO 1200 DIN for a balanced business solution with monitoring, replaceable batteries and useful runtime.
• Choose the CyberPower CP1600EPFCLCD where pure sine-wave output, higher capacity and compatibility with demanding equipment justify the price.

How to size the UPS correctly

1. List every device that will receive battery power.
2. Record or measure each device’s maximum power consumption.
3. Add the watt values together.
4. Include reasonable capacity for peaks and future growth.
5. Determine the required runtime.
6. Check the manufacturer’s runtime curve at the calculated load.
7. Confirm the socket type and number of battery-backed outlets.
8. Verify compatibility with the operating system, server or NAS.
9. Decide whether automatic shutdown is required.

Do not connect high-current equipment such as laser printers to battery-backed outlets unless the UPS manufacturer explicitly allows it.

Evidence for an ISO 27001 implementation

Organizations using a UPS to support Annex A Control 7.11 should retain appropriate evidence, such as:

• the availability risk assessment;
• a list of protected systems;
• the load and runtime calculation;
• the reason for selecting the model;
• installation records;
• configuration of automatic shutdown;
• periodic test records;
• maintenance and battery-replacement records;
• documented actions following failed tests.

A periodic function test and a risk-based runtime test can help identify deteriorating batteries before a real outage occurs. Testing frequency should follow manufacturer guidance and operational requirements.

Conclusion

The best UPS is not necessarily the device with the highest VA rating. It is the model that supports the actual load, provides the required runtime, works with the connected equipment and can be tested and maintained throughout its service life.

For general small-business use, the Eaton Ellipse PRO 1200 DIN offers the most balanced configuration. The CyberPower CP1600EPFCLCD is the strongest technical option in this comparison, particularly where a pure sine-wave output is required. Smaller APC models remain suitable when the load and availability requirements are limited.

Product specifications, prices and availability can change. Always verify the current manufacturer documentation before purchasing. Product links in this article may be replaced with affiliate links in the future.