Final Thoughts and Conclusions

I will admit I came into this review with high expectations. It’s not often we see a 500W power supply with an asking price of $399 USD. However, the FSP Twins is a redundant power supply targeted towards small office and home users for mail or web server systems that require maximum up time. And we need to keep in mind that the Twins 500W redundant power supply has a server-style heritage, which places more emphasis on build quality and reliability and less on tight voltage regulation, low AC ripple, and quiet operation.

The Twins 500W PSU incorporates two 520W modular power supplies inside one standard ATX housing. Under normal operation the two power supplies operate in parallel, sharing the load. If one of the power supply modules should fail, the other one automatically takes over with no down time. And since the power supply modules are hot-swappable, a faulty unit can be replaced without having to turn off the system. I wish that FSP could have designed the system so only one power supply module was active, while the other one remained in standby. This would save wear on the units and help increase efficiency but I understand it is no easy task to expect a standby unit to immediately initialize, stabilize, and take over the load with zero time delay.

First and foremost, the FSP Twins 500W power supply provides added reliability through the redundancy of having two power supplies in one enclosure. During our testing, if one module lost power the other one picked up the load automatically with no interruption or down time. The DC voltage regulation was good, staying within 2% of the target values. While acceptable and well within the ATX guidelines, the AC ripple and noise was higher than we like to see. And not surprisingly, the noise generated by the two 40mm cooling fans is quite loud under mid to high loads. This is not a power supply I would use in a quiet work or home environment. The Twins 500W PSU is backed by a 5-year warranty, which is good, but at this price point a 7-year or even 10-year warranty would be better.

Our biggest disappointment however centers on efficiency. FSP advertises the Twins 500W redundant power supply as being 80 Plus 230V Internal Gold certified. Unfortunately it is not. The two FSP modular power supplies used inside are 80 Plus Gold certified (as long as you power them from 230V mains) but the Twins 500W PSU is not.

During our tests, the FSP Twins 500W redundant PSU only met the 80 Plus Gold criteria for efficiency while operating at 100% load. The criteria are not met at either the 20% or 50% load mark, even when operating on 230V. The reason for this is we are measuring the efficiency of two power supplies operating in parallel, not a single power supply. When testing the Twins 500W power supply, we are testing two modular power supplies sharing the load along with the overhead created by the DC-to-DC converters and other circuits inside the common chassis/frame. For a more detailed explanation of these issues please refer back to the Efficiency section on the previous page.

And last but not least, having a redundant power supply does not address the more common problem of loss of power from the local utility grid. For my money, I’m sticking with a quiet, high-quality desktop power supply and battery-backup UPS.

The FSP Twins 500W redundant power supply is currently available (, and is selling for $399.00 USD. A new Twins 700W model is expected soon.

•    Redundant power supply in the ATX form factor
•    High-quality components and construction
•    Hot-swappable power supply module design
•    Good voltage regulation
•    Digital interface supports FSP Guardian monitoring software
•    Flat ribbon-style cables with two 4+4 pin EPS connectors
•    Protections: OCP, OVP, SCP, FFP (Fan Failure Protection)
•    5-Year warranty
•    Expensive
•    Does not meet 80 Plus Gold efficiency criteria as claimed
•    Modular PSUs operate in parallel instead of keeping one in standby
•    Average AC ripple and noise suppression
•    Noisy 40mm fans

Our thanks to FSP Technology Inc. for sending us the Twins 500W Redundant PSU to review.

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