Uninterruptible Power Supply (UPS): The best to buy

Protecting your computer (and related accessories) from an electrical point of view is of paramount importance, especially if you have invested a lot of money behind your configuration. Voltage fluctuations, disturbances in the line (storms and storms) or sudden lack of electric current and damage is done. Prevention is always better than cure (in this case repair and replace)!

To avoid these and other problems, each PC should be adequately protected from an electrical point of view with an uninterruptible power supply called UPS. How to choose a PC uninterruptible power supply and what are the characteristics it must have? Any doubt will be dissolved in this guide.

What is a UPS?

A UPS allows the equipment to be protected from voltage fluctuations and at the same time allows all the devices connected to it to be kept powered.

When the power comes off the connected devices will remain on for a short time, so as to allow at least to turn them off (even automatically on some models) correctly without losing any data and without suffering damage to the work done so far.

To do this, within the UPS, there is a place:

  • A simple lead-acid battery (usually 12 Volt, like on cars).
  • A power supply, which powers the active current devices and charges the battery at the same time.
  • A rectifier, which stabilizes the incoming AC current (AC) transforming it into a direct current (DC).
  • An inverter, which transforms direct current (DC) into ” clean ” alternating current (AC) that can be used for peripherals, and in case of need (blackout) reverses the current from the battery (DC) into alternating current (AC) for devices.

These components are present in any UPS, what changes is the quality of the electrical signal generated by the devices (as we will see in the next section). For those wishing to deepen the technical discourse on UPS, you can read our technical details.

Type of wave (alternating current)

We can distinguish one UPS from another (and understand, which are the best models) by analyzing the type of wave (alternating voltage) coming out of the UPS and feeding the equipment. This wave is more (from the worst to the best):

  • Quadra (green line)
  • Approximate or pseudo-sinusoidal (blue line)
  • Pure (red line)

The pure sine wave is the best from the point of view of the power supply, but given their cost, we can aim at home also on devices with the approximate wave, able to ensure a good compromise between the quality of the electrical signal and the price of purchase.

Types of UPS (uninterruptible power supply)

After discovering how a UPS works, we find out in detail what differentiates one particular UPS model from the other.


Also called standby, these uninterruptible power supplies are the cheapest ones, they offer a little autonomy, and they come into operation after about 5-10 milliseconds from the blackout, and they do not usually have any kind of protection from possible disturbances or power surges, because the equipment is powered directly from the mains (can also have the shape of a power strip).


Also called double conversion, they are the best continuity units as they come into operation immediately (0.01 milliseconds) and offer total protection. The equipment is powered by a double circuit that includes the battery and the mains, thus preventing disturbances and at the same time stabilizing the current and / or rectifying the voltage in case of need. They can cost a lot, certainly much more than offline, since they are suitable to protect servers and the only disadvantages are the higher consumption and their large size (almost like a PC).


They are a cross between offline and online because they offer superior offline protection while still remaining cheaper than online models. They come into operation after about 5 milliseconds and have a good relationship between price and performance, so they may be the best choice if we have a limited budget and cannot buy an online UPS.

Calculate the VA (VoltAmpere)

The capacity of a UPS is calculated using the VA, a specific unit of measurement.

To calculate the power of the UPS, convert watts to VA or VA to watts using one of the following formulas:

Power (watt) = Apparent power (VA) by power factor.

From this, you get the formula to calculate the power of all electronic equipment (UPS and power supplies included):

Apparent power (VA) = Power (watts) divided by power factor.

The power factor with active PFC power supplies (new models) is generally around 0.9. To calculate then the VA that must have the UPS must divide by 0.9 the wattage of the power supply of the PC:

500w/0.9 = 555.55 VA

If instead we have in our hands a power supply with passive PFC (old models), the power factor is 0.6, so we will have:

500w/0.6 = 833.33 VA

In addition to the watts supplied by the computer, we must obviously add also the watts of the other equipment we want to protect with the UPS: monitors, speakers, modems, routers, scanners, printers ect.

TIP : Laser printers should never be connected to the UPS, because otherwise we need a much more powerful UPS, since a laser printer can also absorb 1500/2000 watts. 


  • A 500 watt PC power supply with active PFC wants at least a 600 VA power supply, with an always 500 watt power supply but with passive PFC, it requires at least a 900 VA UPS (better to round up the wave inaccuracy with passive PFC).
  • The PC has a 600w power supply with active PFC and a power factor of 0.9 and two other 200w devices in total. Converting everything in VA, I get 666 VA for the PC and 333 VA for the peripherals; for the latter, we always use the calculations as if it were a power supply with passive PFC, so we use 0.6 as a power factor. Adding up the values, we find 999 VA of maximum value for all our devices; at this value, we add a good 20% margin for future expansions, so for our system, we need a UPS of at least 1200 VA.

Calculate that a PC rarely runs the power supply at maximum power, so this value will hardly ever be achieved, and we can very well choose a UPS sized to the real consumption of our PC components and peripherals.

The best UPS (uninterruptible power supply)

Below we have collected the top 10 of the best-selling UPS on Amazon. The ranking is constantly updated automatically, every day.

Product prices and availability are subject to change. Any price and availablility information displayed on Amazon at the time of purchase will apply to the purchase of any products.

Back to top button