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FSP Twins 500W Redundant PSU Review

The FSP Twins series combines the usability of a normal ATX PSU and the advanced features of a redundant server unit. The Twins 500W we're evaluating today addresses users that need an ultra-reliable PSU and are willing to pay for it.

Early Verdict

A very interesting PSU that brings the redundant feature to all home users. However the design and implementation needs a number of improvements and the price is probably too high for the majority of buyers.


  • Redundant
  • Digital interface
  • Full power at 45°C
  • Ripple suppression on the minor rails
  • Decent load regulation at +12V
  • Hold-up time
  • Build quality
  • 2x EPS connectors
  • Quality fans
  • Warranty
  • Easy to use software
  • Very strong 5VSB rail


  • Price
  • Efficiency
  • Ripple suppression at +12V
  • Vampire power
  • 3.3V rail performance in Advanced Transient Response tests
  • Non-modular
  • 2x PCIe connectors
  • Noisy

FSP Twins 500W Redudant Power Supply Review

Redundant PSUs, with two or more smaller power supplies, are common in servers. Each PSU in a redundant configuration is able to power the entire system on its own, and usually only one of them runs at a time. If a problem afflicts the primary power source, its back-up takes over almost instantly to ensure no loss of up-time. In addition, you're able to swap out the defective PSU without shutting down.

As you can imagine, redundant PSUs aren't meant for average enthusiasts. They're simply too expensive compared to normal desktop power supplies. But that doesn't mean there shouldn't be a redundant option able to fit in normal ATX cases. This is what inspired FSP's Twins series, which offers redundancy to folks who don't have a problem spending lots of money to safeguard against power issues.

Currently, the FSP Twins family only includes one member. Soon there will be a 700W model, though. Today we're reviewing the Twins 500W, which, as its name suggests, consists of two modules capable of delivering up to 500W each. Interestingly, both PSUs can operate in parallel to increase efficiency under moderate and high loads.

You could say that running two PSUs at the same time defeats the purpose of redundancy, since they could both break down. Though that's highly unlikely, we do believe FSP should provide the option to disable parallel operation of both modules for anyone who wants to be sure they'll have backup in the event of a problem. This would also increase efficiency under light loads.


The Twins 500W consists of a main chassis (frame) and two power modules. The frame's maximum power is 500W according to its paper specs, while each module can deliver up to 520W on the +12V rail. FSP's modules are 80 PLUS Gold-certified, and it's notable that they are certified with 230V input instead of 115V, where efficiency is lower. 80 PLUS includes the modules in its 230V Internal category because they are used in server PSUs. In our opinion, since this PSU employs a distinctive design where both power modules operate in parallel, it should be evaluated by the 80 PLUS program as it is. After all, when you combine two PSUs, their efficiency is naturally lower under light loads. In this case, though, the certification was based on the efficiency of each module, as if they operated alone and not in parallel.

All cables are fixed, and because this is a server-like product, its maximum operating temperature for continuous full power delivery is 50°C. FSP doesn't mention over-temperature protection in its feature list, but according to our test results OTP is supported. That's great, of course; we cannot imagine a server PSU without OTP. FSP also has a capability called fan failure protection. When the system detects a fan problem, the corresponding module shuts down and a loud noise is emitted from the frame's buzzer.

Cooling is handled by a couple of small, 40mm, double-ball bearing fans. Each one blows air through a module, and there is no semi-passive mode, so the fans spin constantly. They are, however, thermally controlled, so under light loads the acoustic output is reasonable for a server PSU.

The Twins 500W is covered by a satisfactory five-year warranty. It measures 19cm deep, meaning it's not particularly compact. But most full- and mid-tower ATX cases should accommodate it without an issue.

Power Specifications

Max. PowerAmps202016161630.5
Total Max. Power (W)500

The frame has three +12V rails and its DC-DC converters can deliver up to 130W on the minor rails. Meanwhile, the 5VSB rail has 3A maximum current output, though its real capabilities are much higher since OCP is set at 10A!

Cables And Connectors

Native Cables
DescriptionCable CountConnector Count (Total)Gauge
ATX connector 20+4 pin (485mm)1116AWG
4+4 pin EPS12V (600mm)2218AWG
6+2 pin PCIe (460mm+150mm)1218AWG
SATA (450mm+150mm+150mm+150mm)1418AWG
SATA (450mm+150mm) / Four-pin Molex (+150mm+150mm)12 / 218AWG
USB Header Female (520mm)11-
USB Header Male to USB Male Adapter  (270mm)11-
FDD Adapter (+100mm)1122AWG

All cables are fixed, unfortunately, and the number of PCIe connectors is limited to two. On top of that, the six SATA connectors might not be enough for folks with a lot of hard drives and SSDs. Given the non-modular design, though, more cables would make installation a pain. Thankfully, the Berg connector is provided in an adapter form. There is also a USB cable for connecting the frame with the system to communicate with FSP's Guardian software.

Power Distribution

12V1EPS1, Peripheral, SATA

There are three +12V rails and power distribution looks good, since both EPS connectors are separated from the PCIe ones.

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Aris Mpitziopoulos
Aris Mpitziopoulos

Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.

  • shrapnel_indie

    Full power at 45°C
    All cables are fixed, and because this is a server-like product, its maximum operating temperature for continuous full power delivery is 50°C.

    Please explain to me why these numbers don't seem to match up properly. (THB, I may have missed it.)

  • dstarr3
    I really wonder what a consumer could possibly want this for. What is an ordinary consumer doing that they absolutely cannot risk any downtime whatsoever on their rig?
  • nzalog
    I know freenas can be configured to work faster if you can for sure trust the system from not having RAM errors (covered by ECC) and if you can guarantee there is no unexpected shutdown (covered by dual power and ups). However the reliable power is not really required because a SSD as an SLOG device will cover for it, but then the SSD becomes the bottleneck for writes.
  • firefoxx04
    I build several file servers a month for clients. Low end enough to where pre built solutions are not an option. This power supply would be a good fit but it is useless, imo, without some sort of email alert option. Maybe I missed that?

    When I deploy file servers for clients, I always setup some sort of alert system for raid failures so I can fix the problem. What is the point of redundancy if the user has no idea a problem has occurred? Yes i know that this PSU makes a "loud buzzer noise" but I cant have that either. The user needs to continue to use the system and they cannot if it is screaming 100% of the time.

    Send me an email alert. Its easy to implement.
  • Rookie_MIB
    One thing I'm curious about - what if one unit does fail? Are they bog-standard replacement parts where you can go and buy a similar hot swap redundant power supply or is the system proprietary. If it's the latter, then I don't see many people lining up for this one...
  • apache_lives
    A PSU is but one part of a "reliable" machine, to me this will not increase up time or do anything of any value, seems more like a "makes me feel better" part.
  • Aris_Mp
    about the first comment, the PSU is certified for up to 50C ambient full power delivery, but I choose to test up to 45C every PSU that passed from my test bench (since I also have to evaluate 40C rated units and I need to keep the same conditions for all).
  • PsiReaper
    A perfect PSU upgrade for my UnRAID box..
  • shrapnel_indie
    19144735 said:
    about the first comment, the PSU is certified for up to 50C ambient full power delivery, but I choose to test up to 45C every PSU that passed from my test bench (since I also have to evaluate 40C rated units and I need to keep the same conditions for all).

    While I'm glad for that, It's also nice to know if a unit rated at 50°C operation will deliver on its "promise" though. (If you exceed the "promised" rating, like the 40°C rated units @ 45, well, it delivered on its promise and then some.)

  • Pompompaihn
    Newegg has several server chassis for sale that come WITH redundant 500w+ PSUs for less money than just this power supply. Given that the market is low end commercial/prosumer, and it's not going to be for gaming or HTPC, why wouldn't you just buy the whole thing for cheaper?