The power supply worked normally with an APC SmartUPS SC 620 under loads up to 370W irrespective of the power source (electric mains or batteries). The UPS switched to its batteries without problems.

The cross-load characteristics of the 600W unit don’t look too pretty, but are acceptable. The +5V voltage is not very stable, but fits into the green zone within the load range typical of modern computers, i.e. 20-50W. The +12V voltage is set higher than necessary and is going to be 2-3% above the nominal value in a real computer. It deflects by 5% from the nominal – the maximum permissible deflection – only when there’s high load on the +5V and +3.3V rails, which is insignificant for today’s PCs.

It’s worse with the 700W model. Its +3.3 voltage fluctuates wildly through the diagram, making it rather untidy, with ragged borders and a lot of red color. Well, it’s all normal within the area that is the most important for a modern computer system, but anyway. This cross-load diagram is acceptable and nothing more. Moreover, there’s quite a lot of PSUs with group voltage regulation (like in the GameXCtream) that show better results in this test.

The two models don’t differ much in terms of output voltage ripple. The oscillogram above is for the senior model: 25 millivolts on the +5V rail, 81 millivolts on the +12V rail, and 28 millivolts on the +3.3V rail. That’s all within the norm. Only high-frequency pulsation is present.

Protechnic Electric MGA12012HB-O25 fans are installed in both models. These are the same fans as in the original PSUs from FSP. They have gained a reputation of average-quality fans among the users. Some users have reported that the fan blades are buzzing audibly in their samples of the PSU.

I was very pleased with very quiet operation of FSP Epsilon power supplies, but the OCZ GameXStream is just the opposite. Even under minimum load the fan speed is over 1300rpm, and it grows up to 2200rpm at the maximum. The fan speed graphs of the 600W and 700W models almost coincide so I only publish the graph of the senior model above.

The efficiency of the PSUs is high. It reaches 87% at one point with the 700W model, the average being about 86%. The 600W model has an efficiency of 84-84%.

So, while the FSP Epsilon units left very good impressions on me, I am rather disappointed with the new PSUs from OCZ. Although they do not in fact differ from the Epsilons, and even have absolutely the same fans (for example, Zalman replaces the original fans in its PSUs, which are too manufactured by FSP, with quieter ones), they are rather noisy at work and do not have high voltage stability. I can’t say if all other PSUs produced for OCZ are like that or if only the Epsilon series is (and if yes, then it may be just models produced at a certain time period) because FSP Group’s representatives didn’t answer to my inquiries. So, be careful when shopping. Well, if you can choose between these two PSUs and other models described in this review, you should instead consider the products under the brands of Seasonic, Corsair or Zalman, even though the latter company buys its PSUs from FSP, too. If you are choosing between FSP Epsilon and OCZ GameXStream PSUs, you should be aware that these two series differ only in the name on the label. So, you may want to choose what is cheaper.