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Seasonic SS-300SFD

The next product is a variant of the SFX12V standard. There are as many as five such variants in existence today, and they are not even compatible with each other.

The SS-300SFD represents “SFX12V with a top-mount fan”. The variant owes its name to the 80x80x25mm fan which is large for such a compact PSU and sticks out of its case a little.

There are SFX12V products without the protruding fan. For example, the Silverstone Sugo SG06 is equipped with a FSP300-60GHS which features a 15mm-thick fan which fits within the case. In other words, there are two sub-variants of one of the five SFX12V variants, and these two are not even fully compatible. The SS-300SFD will not fit into some system cases where the height of the PSU is a critical factor.

The interior design is more alike to traditional ATX power supplies than that of the above-discussed SS-250SU. There is a heatsink with the power transistors of the converter and active PFC on the right. The diodes of the output rectifier are on the left. The power transformer is in the middle. Still, the component density is impressively high.

Quite a lot of components reside on the bottom side of the PCB. The quality of soldering is next to ideal, as you can note.

The PSU is cooled with an ADDA AD0812HB-A70GL fan (80x80x25 mm; 3010 RPM). The fan is perfectly standard and has a popular form-factor, so you can easily replace it if necessary.

This PSU is equipped with the following non-detachable cables:

  • One mainboard cable with a 20+4-pin connector (32 cm)
  • One CPU cable with a 4-pin connector (32 cm)
  • Two cables with two PATA power connectors and one floppy-drive plug on each (34+16+16 cm)
  • One cable with two SATA power connectors (28+14 cm)

Computers with gaming graphics cards are but seldom equipped with such PSUs, yet I know such examples, therefore it is regrettable that the SS-300SFD lacks 6-pin graphics card connectors. It would also be better to replace one of its two PATA power cables with a SATA one.

Working with my APC SmartUPS SC 620, this power supply was stable at loads up to 270 watts (also when switching to the batteries and back again). The UPS would become unstable at 280 watts and would shut down immediately at a load of 300 watts as soon as it tried to switch to the battery power. Thus, this PSU calls for a reserve of power on the side of your UPS.

The PSU can deliver almost all of its output power across the +12V rail but also supports high loads on the +5V and +3.3V rails as well as on the standby source.

The output voltages were not ideally stable (this PSU does not have dedicated voltage regulation, after all), yet I am quite satisfied with them. Our test configuration (including a rather fast Radeon HD 4850 graphics card) is in the green zone where the voltages deflect no more than 1% from their nominal values. The PSU copes with very low loads well, too.

The high-frequency ripple of the output voltages is much lower than the permissible maximums.

The low-frequency voltage ripple is very low.

The PSU features 80+ certification and meets it indeed: its efficiency is over 81% at loads from 50 to 300 watts.

The fan controller keeps the fan speed constant at 1250 RPM, which is almost silent, when the load (and temperature) of the PSU is low. When the load is higher than 130 watts, the speed of the fan increases linearly. The PSU becomes audible at 200-220 watts and noisy at over 250 watts.

The standby source is okay. Its voltage sags by a mere 0.1 volts at a load of 2 amperes.

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