Seasonic SS-350TGM 80 Plus Gold TFX

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TFX power supply
Sample Supplier
Seasonic USA
Seasonic Electronics

It is ironic that while the average power demand of desktop CPUs has dropped dramatically so that they now rarely draw more than 10W at idle, the average computer power supply rating has gone in the opposite direction. Kilowatt and higher rated power supplies abound more than ever, and there are only a handful of name-brand retail ATX PSUs rated at below 450W. On the other hand <150W DC/DC converter boards with external AC/DC power adpters have become the norm for SFF computers. But if you want a quality power supply built into a modern, compact PC, the 200~400W area is barren.

The SS-350TGM and 300TGM TFX power supplies from Seasonic fit into this niche. Their combination of modest power and 80 Plus Gold ratings is rare in the retail market, where most 80 Plus Gold PSUs are at least 400W, and more commonly 600W or higher. It is not so unusual among PSUs made specifically for big OEMs, who rarely pay for unnecessarily high powered PSUs. The TFX form factor means that the TGM series PSUs cannot be dropped in as a replacement for any ATX power supply, however; it is housed in a smaller, but longer-shaped housing.

TFX power supplies are also uncommon in retail cases, although the Antec NSK1480 HTPC case we reviewed a couple years ago comes to mind. They are much more widely used by big system integrators in SFF or low profile systems. Current PCs that utilize TFX power supplies include the HP Pavilion Slimline series (model s5xt, for example) and most Dell Slim Tower models (such as the Inspiron 620 ST). Going back to retail component markets, the class of cases Newegg refers to as MicroATX Slim are similar in size and shape to the aforementioned slim PCs. The selection of such cases is not large, and they tend to be basic, low-cost products that usually come with a PSU.

Our Seasonic SS-350TGM TFX PSU sample came without any retail packaging, as befits a product that will be used mostly by system integrators.


The SS-350TGM is painted classic battleship grey. As with the vast majority of PSUs in the TSX form factor, the cooling fan is 80mm in diameter.

The SS-350TGM sports the typical OEM color: Grey. An 80mm cooling fan at a right angle to the small vent at one end of the casing, as per the TSX norm. The intake vent over the fan is about average, probably blocking ~20% of the potential airflow. There is no power switch.

Here is a major departure from the norm: Totally detachable output cables. In the past, Seasonic was reluctant to use them on lower power PSUs, citing losses in the contacts as hurdles to high efficiency. My guess is that the technology developed in the X series has helped Seasonic overcome this challenge.

All the output cables are on a single assembly, without sleeving.

The cables are appropriately short, because TSX PSUs are usually used in small cases. Provided are connectors for four SATA drives, two old 4-pin Molex, a floppy drive, the main 24-pin ATX and a 4-pin AUX12V. (Note: The 4-pin AUX12V will work even in an 8-pin AUX12V motherboard socket.)

The low voltage lines get 80W total (plenty for a modern PC) while almost the entire rated power is available on 12V (as it should be), split on two rails. My guess is that the AUX12V is on one rail while the rest of the outputs share the other 12V rail.

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