The cross-load diagram of the junior model resembles the FSP Epsilon. The +12V voltage is higher than necessary and not very stable while the +5V and +3.3V voltages go below the acceptable limit when the load grows on the respective power rails. This PSU is going to cope with a modern PC that puts but a small load on the latter two rails, but it does not comply with its own specifications.
The 600W model is somewhat better, but not ideal, either. The +5V voltage bottoms out heavily when there is a high load on the appropriate rail while the +12V voltage is much higher than the nominal value when the load on the +12V rail is low. The PSU is going to power the PC all right, yet diagrams with more green, rather than with yellow or red, are much more agreeable to my eye.
The output voltage ripple isn’t strong. It is much lower than allowable on each of the three tracked power rails even at maximum load.
Both PSUs make use of Adda AD1212MB-A71GL fans (120x120x25mm, 2050rpm). The rated speed is rather low, promising low noise.
In the junior model the fan started from 940rpm and was accelerating steadily and linearly at higher loads. It did so not too fast, however. The maximum of speed is only 1350rpm. This indicates a quiet PSU although I guess the fan might have started to accelerate from a certain load only to make the PSU even quieter.
In the ZM600-HP the fan started out from 1000rpm and stopped at 1600rpm. This is somewhat worse than in the ZM500-HP but still good. The PSU is not silent at low loads but the fan speed is being increased less rapidly at higher loads than in many other PSUs.
Each model has a good efficiency that quickly reached 86% as the load grew and then kept around that value until a load of 400W and higher when it dropped to 83%.
Thus, the high-wattage power supplies from Zalman are not good in only one parameter, in the stability of the output voltages. They share this problem with the FSP Epsilon PSUs but they are not as noisy as the products from FSP Group, having less powerful and high-quality fans. They also feature detachable cables. I can’t recommend these PSUs as the best buy due to the mentioned problem, yet you may want to consider them if silence is your priority. And if your system consumes no more than 350-400W at full load, you may even want to consider the lower-wattage ZM460B-APS that we tested earlier.