[nextpage title=”Introduction”]

CX400W is the simplest power supply offered by Corsair, featuring active PFC, a 120 mm fan on its bottom, single-rail design and costing only around USD 50. Is it a good product? Let’s see.

Like most power supplies from Corsair, CX400W is manufactured by Seasonic (Corsair HX750W, HX850W and HX1000W are manufactured by CWT). Internally this power supply uses the same design as Corsair VX450W, Antec EarthWatts 500 W and Arctic Cooling Fusion 550RF as we will explain.

Corsair CX400W power supplyFigure 1: Corsair CX400W power supply.

Corsair CX400W power supplyFigure 2: Corsair CX400W power supply.

Corsair CX400W is a small power supply, being 5 ½” (140 mm) deep, using a 120 mm fan on its bottom and featuring active PFC.

Being an entry-level product it doesn’t have a modular cabling system. All cables have a nylon protection that comes from inside the power supply. The included cables are:

  • Main motherboard cable with a 20/24-pin connector.
  • One cable with two ATX12V connectors that together form one EPS12V connector.
  • One auxiliary power cable for video cards with one six-pin connector.
  • Two SATA power cables with three SATA power connectors each.
  • Two peripheral power cables with three standard peripheral power connectors and one floppy disk drive power connector each.

The number of cables is enough for you to build a mainstream PC, and this is the exact same cable configuration found on Corsair VX450W.

All wires are 18 AWG, which is the correct gauge to be used. All cables are very long, measuring 23 5/8” (60 cm) between the power supply and the first connector on the cable, and then 6” (15 cm) between each connector on the cable on cables that have more than one connector. So you can easily install it inside a full tower case.

Corsair CX400W power supplyFigure 3: Cables.

Now let’s take an in-depth look inside this power supply.

[nextpage title=”A Look Inside The CX400W”]

We decided to disassemble this power supply to see what it looks like inside, how it is designed, and what components are used. Please read our Anatomy of Switching Power Supplies tutorial to understand how a power supply works and to compare this power supply to others.

This page will be an overview, and then in the following pages we will discuss in detail the quality and ratings of the components used.

As mentioned, internally Corsair CX400W uses the same design as Corsair VX450W, Antec EarthWatts 500 W and Arctic Cooling Fusion 550RF.

Corsair CX400W power supplyFigure 4: Overall look.

Corsair CX400W power supplyFigure 5: Overall look.

Corsair CX400W power supplyFigure 6: Overall look.

[nextpage title=”Transient Filtering Stage”]

As we have mentioned in other articles and reviews, the first place we look when opening a power supply for a hint about its quality, is its filtering stage. The recommended components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor), and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components, usually removing the MOV and the first coil.

The transient filtering stage from this power supply is flawless, providing one X capacitor, two Y capacitors and one ferrite coil more than required. This is really nice to see, especially on an entry-level product.

Corsair CX400W power supplyFigure 7: Transient filtering stage (part 1).

Corsair CX400W power supplyFigure 8: Transient filtering stage (part 2).

This stage is identical to the one used on Corsair VX450W, Antec EarthWatts 500 W and Arctic Cooling Fusion 550RF.

In the next page we will have a more detailed discussion about the components used in the Corsair CX400W.

[nextpage title=”Primary Analysis”]

On this page we will take an in-depth look at the primary stage of Corsair CX400W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU806 rectifying bridge in its primary, which can deliver up to 8 A at 100° C. This component is clearly overspec’ed: at 115 V this unit would be able to pull up to 920 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 736 W without burning this component. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

On the active PFC circuit two FDP18N50 power MOSFET transistors are used, each one capable of delivering up to 18 A at 25° C or 10.8 A at 100° C in continuous mode (note the difference temperature makes), or up to 72 A in pulse mode at 25° C. These transistors present a resistance of 265 mΩ
when turned on, a characteristic called RDS(on). This number indicates the amount of power that is wasted, so the lower this number the better, as less power will be wasted thus increasing efficiency.

Corsair CX400W power supplyFigure 9: Active PFC transistors and diode.

This power supply uses a Japanese capacitor from Hitachi labeled at 85° C to filter the output from the active PFC circuit.

In the switching section, two FQP13N50C power MOSFET transistors are used on the traditional two-transistor forward configuration. Each one is capable of delivering up to 13 A at 25° C or 8 A at 100° C in continuous mode (note the difference temperature makes), or up to 52 A in pulse mode at 25° C. These transistors present an RDS(on) of 480 mΩ (too high in our opinion).

Corsair CX400W power supplyFigure 10: Rectifying bridge and switching transistors.

The rectifying bridge is the same model used on Corsair VX450W, Antec EarthWatts 500 W and Arctic Cooling Fusion 550RF, however the PFC and switching transistors from CX400W’s primary have lower current limit.

The primary is controlled by the “famous” CM6800 PFC/PWM combo controller.

Corsair CX400W power supplyFigure 11: PFC/PWM combo controller.

Now let’s take a look at the secondary of this power supply.

[nextpage title=”Secondary Analysis”]

This power supply uses four Schottky rectifiers on its secondary. The secondary from Corsair CX400W is absolutely identical to the secondary from Corsair VX450W, Antec EarthWatts 500 W and Arctic Cooling Fusion 550RF. So the main difference between Corsair CX400W and these other power supplies are the transistors used on the primary.

The maximum theoretical current each line can deliver is given by the formula I / (1 – D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode. Just as an exercise, we can assume a typical duty cycle of 30%.

The +12 V output is produced by two SBR30A50CT (30 A, 15 A per internal diode at 110° C, maximum voltage drop of 0.55 V) connected in parallel. This gives us a maximum theoretical current of 43 A or 514 W for the +12 V output.

By the way, we are now talking about the voltage drop presented by the rectifiers. This parameter shows how much voltage is wasted by the rectifier. The lower this number is, the better, as less voltage is wasted, increasing efficiency.

The +5 V output is produced by one STPS30L30CT Schottky rectifier (30 A, 15 A per internal diode at 140° C, maximum voltage drop of 0.57 V), giving us a maximum theoretical current of 21 A or 107 W for this output.

The +3.3 V output is produced by another STPS30L30CT Schottky rectifier, giving us a maximum theoretical current of 21 A or 71 W for this output.

All these numbers are theoretical. The real amount of current/power each output can deliver is limited by other components, especially by the coils used on each output.

Corsair CX400W power supplyFigure 12: Rectifiers.

The secondary is monitored by an HY510N integrated circuit, which is installed on a small daughterboard and provides under voltage (UVP) and over voltage (OVP) protections. Any other protection that this unit may have is implemented outside this integrated circuit.

Corsair CX400W power supplyFigure 13: Monitoring integrated circuit.

Most electrolytic capacitors from the secondary are from OST. Here is a smaller difference between CX400W and VX450W: VX450W uses Japanese caps here.

[nextpage title=”Power Distribution”]

In Figure 14, you can see the power supply label containing all the power specs.

Corsair CX400W power supplyFigure 14: Power supply label.

Since this power supply uses a single-rail design, there is nothing to talk about here.

Now let’s see if this power supply can really deliver 400 W.[nextpage title=”Load Tests”]

We conducted several tests with this power supply, as described in the article Hardware Secrets Power Supply Test Methodology.

First we tested this power supply with five different load patterns, trying to pull around 20%, 40%, 60%, 80%, and 100% of its labeled maximum capacity (actual percentage used listed under “% Max Load”), watching how the reviewed unit behaved under each load. In the table below we list the load patterns we used and the results for each load.

If you add all the power listed for each test, you may find a different value than what is posted under “Total” below. Since each output can vary slightly (e.g., the +5 V output working at +5.10 V), the actual total amount of power being delivered is slightly different than the calculated value. On the “Total” row we are using the real amount of power being delivered, as measured by our load tester.

+12V1 and +12V2 are the two independent +12V inputs from our load tester and during our tests they were connected to the single +12 V rail available on the tested power supply.

Input Test 1 Test 2 Test 3 Test 4 Test 5
+12V1 2.5 A (30 W) 5.5 A (66 W) 8 A (96 W) 10.5 A (126 W) 14 A (168 W)
+12V2 2.5 A (30 W) 5.5 A (66 W) 8 A (96 W) 10.5 A (126 W) 13 A (156 W)
+5V 1 A (5 W) 2 A (10 W) 4 A (20 W
)
6 A (30 W) 8 A (40 W)
+3.3 V 1 A (3.3 W) 2 A (6.6 W) 4 A (13.2 W) 6 A (19.8 W) 8 A (26.4 W)
+5VSB 1 A (5 W) 1 A (5 W) 1.5 A (7.5 W) 2 A (10 W) 2 A (10 W)
-12 V 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W) 0.5 A (6 W)
Total 79.3 W 159.6 W 238.5 W 317.0 W 402.9 W
% Max Load 19.8% 39.9% 59.6% 79.3% 100.7%
Room Temp. 45.8° C 45.5° C 45.2° C 45.9° C 49.0° C
PSU Temp. 48.3° C 48.0° C 48.3° C 48.8° C 54.5° C
Voltage Stability Pass Pass Pass Pass Pass
Ripple and Noise Pass Pass Pass Pass Pass
AC Power 97.6 W 190.3 W 285.0 W 383.8 W 500.2 W
Efficiency 81.3% 83.9% 83.7% 82.6% 80.5%
AC Voltage 112.4 V 111.6 V 111.7 V 110.6 V 109.2 V
Power Factor 0.983 0.990 0.994 0.996 0.996
Final Result Pass Pass Pass Pass Pass

Corsair CX400W presents a very good efficiency for an entry-level product. If you pull between 40% and 60% from its labeled capacity (between 160 W and 240 W) you will see efficiency of almost 84%. Pulling around 80% from its maximum (320 W) efficiency was 82.6%. At light load (20%, i.e., 80 W) and full load (400 W) efficiency dropped, but still above the 80% mark.

Voltage stability is another highlight from this product. All voltages (except -12 V) were within 3% from their nominal value, whereas the ATX specification says they must be within 5%. Translation: voltages were closer to their nominal values than needed.

Ripple and noise were extremely low. With this power supply delivering 400 W noise level at +12 V outputs were less than a quarter of the maximum allowed. You can see the results for test number five below. All numbers are peak-to-peak figures and the maximum allowed is 120 mV for the +12 V outputs and 50 mV for the +3.3 V and +5 V outputs.

Corsair CX400W power supplyFigure 15: +12V1 input from load tester at 402.9 W (26.6 mV).

Corsair CX400W power supplyFigure 16: +12V2 input from load tester at 402.9 W (29.6 mV).

Corsair CX400W power supplyFigure 17: +5V rail with power supply delivering 402.9 W (18.2 mV).

Corsair CX400W power supplyFigure 18: +3.3 V rail with power supply delivering 402.9 W (16.4 mV).

Let’s see if we could pull more than 400 W from this unit.

[nextpage title=”Overload Tests”]

Before overloading a power supply we always test to see if over current protection (OCP) is active and at what current level it is triggered. OCP entered in action when we tried pulling more than 36 A from the +12 V rail.

Then starting from test five we increased currents to the maximum we could with the power supply still running inside ATX specs. The results are below.

The idea behind of overload tests is to see if the power supply will burn/explode and see if the protections from the power supply are working correctly. This power supply didn’t burn and when we tried to pull far more than it could deliver it would shut down, so this unit passed on this test.

As you can see Corsair could have labeled this unit as a 450 W product, but they decided not to do so probably because of efficiency, which drops below 80% if we pull more than 400 W from it.

Input Maximum
+12V1 15 A (180 W)
+12V2 15 A (180 W)
+5V 13 A (65 W)
+3.3 V 13 A (42.9 W)
+5VSB 2 A (10 W)
-12 V 0.5 A (6 W)
Total 483.9 W
% Max Load 120.6%
Room Temp. 49.0° C
PSU Temp. 54.5° C
AC Power 616.0 W
Efficiency 78.3%
AC Voltage 107.8 V
Power Factor 0.998

[nextpage title=”Main Specifications”]

Corsair CX400W power supply specs include:

  • ATX12V 2.2
  • Nominal labeled power: 400 W at 40° C.
  • Measured maximum power: 483.9 W at 49.0° C.
  • Labeled efficiency: 80% minimum (80 Plus certified).
  • Measured efficiency: Between 80.8% and 85.5% at 115 V (nominal, see complete results for actual voltage).
  • Active PFC: Yes.
  • Modular Cabling System: No.
  • Motherboard Power Connectors: One 20/24-pin connector and two ATX12V connectors that together form an EPS12V connector.
  • Video Card Power Connectors: One six-pin connector.
  • Peripheral Power Connectors: Six in two cables.
  • Floppy Disk Drive Power Connectors: Two.
  • SATA Power Connectors: Six in two cables.
  • Protections: Information not available. Over current (OCP) and short-circuit (SCP) protections (SCP) present and working.
  • Warranty: Three years.
  • Real Manufacturer: Seasonic
  • More Information: https://www.corsair.com
  • Average price in the US*: USD 49.99.

* Researched at Newegg.com on the day we published this review.

[nextpage title=”Conclusions”]

Corsair CX400W is an excellent product for the regular user that is building a PC with just one video card. It provides enough cables and they are long, allowing you to easily install this power supply inside a full tower case.

Efficiency was great for an entry-level product, peaking almost 84%. Voltages were very close to their nominal values and ripple and noise were practically non-existent.

Internally Corsair CX400W is similar to Corsair VX450W, Antec EarthWatts 500 W and Arctic Cooling Fusion 550RF, but using less power transistors on the primary.

Costing only USD 50, it provides an outstanding cost/benefit ratio. If you are building a mainstream PC and are not thinking of installing a very high-end video card you can buy this power supply with your eyes closed.