The PSU maintains stability on both +12V and +5V rails superbly. It’s head above the above-described models in this parameter and closely approaches PSUs with dedicated voltage regulation.
The ZM400B controls the fan rotation speed smoothly, without those discrete steps as we have seen with the PN(PF) series. The max rotation speed is only 2050rpm. As a result, the fan is quiet even at full load, despite its small size (80mm, but it’s a quality thing – NMB 3110GL-B4W-B30).
On the other hand, the use of a small fan worsens not only the cooling of the PSU proper, but also the ventilation of the whole system case, so you may want to put additional system fans into your computer. But two low-speed fans are anyway much quieter than a high-speed one.
The efficiency factor of this model is higher than that of the previous models, but it couldn’t hit the 80% mark anyway. The power factor, despite the active PFC device, isn’t impressive. Those 0.93-0.94 look good against PSUs with passive PFC, but not too well against many other models with active PFC.
In my earlier review I called this PSU an excellent choice for top-end computers, but things have changed since then. PSUs of the ATX12V 2.0 standard are widely available now and suit much better for the latest generation of computer systems. Thus, the ZM400B-APS, a.k.a. FSP400-60PFN, is still a high-quality and quiet PSU with excellent characteristics, but I wouldn’t now recommend it for today’s top-end computers. Such computers may put a higher load on the +12V rail than this PSU can sustain. The ZM400B-APS is also going to make a good PSU for powerful last-generation systems based around the Socket A platform with a mainboard that powers the CPU via the +5V rail. A high load on this rail leads to a distortion of the output voltages with many PSUs, while the ZM400B-APS is going to handle this situation without problems.