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.

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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