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Enermax MODU87+ (EMG800EWT)

Enermax once gathered my praises for its MODU82+ and PRO82+ series products (the number in the name denotes the bottom efficiency in the typical load range).

Today, I am going to discuss the further development of the MODU series, the MODU87+ power supply. As you may guess from its name, it is expected to be over 87% efficient!

The PSU comes in a medium-sized box with a huge “80+Plus Gold” label forming the background. This is the top level of the 80+Plus certification this PSU is supposed to comply with.

Exterior Design

The prestigious status of the product is expressed in its appearance, especially in the shining gold impeller of the fan.

The MODU87+ is a modular power supply. It has five connectors for peripheral power cables and three combined connectors for graphics card cables. The latter are a special pride of Enermax since the 12-pin connector has a higher load capacity and can be used to connect cables with two end connectors.

Enermax also offers the PRO87+ series which has the same parameters but lacks detachable cables. If you don’t need the modular design, you may want to prefer the PRO87+ series because it is somewhat cheaper.

A few minor but interesting details can be spotted in the appearance of this power supply.

The metal around the fan is shaped in such a way as to reduce the gap between the fan and the case. Enermax engineers argue that this helps lower the noise by 1-2 dB. Interestingly, I have seen this solution in Enermax power supplies before, but implemented in a different way. And I have also seen this exact shaping of the case in PSUs from OCZ and Chieftec! Is it a coincidence or deliberate borrowing? Or could it be the result of one manufacturer working for multiple clients?

I was at first puzzled by the invitation to glue the Enermax sticker to the PSU with my own hands (the sticker is included with the PSU). Why didn’t they do that at the factory? The answer is simple: you can glue the sticker depending on how the PSU is positioned in your system case so that the name of the manufacturer is not upside down.

This solution still does not account for system cases with a vertical position of the PSU (such as some large HTPCs), but I guess that most users don’t care at all what labels there are at the back of their computer.

Take note of the two grooves in the case below the mains connector. You are supposed to insert this wire bracket into them:

The bracket serves as a cable holder and prevents the mains cable from unplugging if someone just pulls at it. You may appreciate this feature if you’ve got a restless dog or a small child in your home.

Interior Design

The MODU87+ looks like an ordinary modern PSU with active PFC and dedicated voltage regulation based on DC-DC converters. However, the manufacturer lists the so-called resonance topology of the main transformer among its features. You can identify it by the extra choke which is missing in other PSUs.

This topology does not bring anything interesting to end-users, though. A resonance transformer is a control circuit that minimizes switching loss by switching transistors at near-zero levels of voltage and current (such PSUs are often referred to as ZVS/ZCS or Zero Voltage Switching and Zero Current Switching). Resonance-topology power supplies are produced by Enermax and other firms already, e.g. by FSP (you can find them at shop selling under the brands of Silverstone, Zalman, etc).

Compared to an ordinary transformer, a resonance transformer has an extra choke and capacitor with such characteristics that the resonant frequency of this LC circuit matched the time period during which the inverter's transistors are open. Thus, in an ordinary transformer, the current grows up linearly when the transistors are open and reaches its maximum at the moment of switching off, but in a resonance transformer the current is sinusoidal, reaching its maximum in the middle of the cycle and lowering to zero by the time the transistors must close. The document Power Semiconductor Applications: Switched Mode Power Supplies by NXP Semiconductors explains this in detail and in comprehensible language (for those who know the basics of switching power supplies, of course) on page 219 (117).

By the way, as the period during which the transistors are open must not change in resonance mode, resonance transformers are controlled by means of pulse frequency modulation (PFM) rather than pulse width modulation (PWM),

The lower loss on the transistors means higher efficiency, lower heat dissipation and lower EMI from the PSU. However, it does not affect the output parameters of the PSU. So, if you don't care much about how efficient your PSU is, models with resonance transformer won’t have any special appeal to you.

As noted above, the PSU produces +5V and +3.3V voltages by means of two full-featured DC-DC converters but, unlike in the Revolution series products, these converters are mounted on the main PCB rather than on the card with output connectors. Two narrow cards with capacitors can be seen nearby: this solution helps achieve the required capacitance and save space. Both electrolytic (KZE series from United Chemi-Con) and solid-state capacitors are used here.

And finally, here is one more peculiarity in the assembly of this PSU. High-load conductors of a PCB are usually tin-plated in order to reduce loss (this is often done in a grid-like pattern as can be seen in the top left of the photo). When solder alone is not enough, a piece of naked copper wire is laid along the conductor and covered with solder as well. The engineers went further with the MODU87+: there are whole copper plates soldered to and shaped like the conductors.


The PSU is rated for an output power of 800 watts and can yield 792 watts via its +12V power rail which is split into four “virtual” output lines. The load capacity of the +5V and +3.3V rails is rather low, but modern computers hardly ever need more than 50 watts out of them, so the available 120 watts should be enough for any real-life situation.

Cables and Connectors

The PSU is equipped with the following cables and connectors:

  • Mainboard cable with a 24-pin connector (58 cm)
  • CPU cable with a 4+4-pin connector (57 cm)
  • CPU cable with an 8-pin connector (57 cm)
  • Two graphics card cables with one 6+2-pin connector on each (45 cm)
  • Three connectors for graphics card cables
  • Five connectors for peripheral power cables

Included with the PSU are:

  • Two graphics card cables with two 6+2-pin connectors on each (49 cm)
  • One cable with four PATA power connectors and one floppy-drive plug (45+15+15+15+15 cm)
  • Two cables with two PATA and two SATA power connectors on each (45+15+15+15 cm)
  • Two cables with four SATA power connectors on each (45+15+15+15 cm)

This selection of connectors should be all right for most configurations but I guess that most users won’t need two separate CPU power cables. One of them might have been made detachable, especially as one of the three connectors for graphics card cables is going to be unoccupied if you use the included cables only.

UPS Compatibility

Working with my APC SmartUPS SC 620, this power supply was stable at loads up to 390 watts when powered by the mains and up to 355 watts when powered by the batteries. They had no problems switching to the UPS’s batteries.

Output Voltage Stability


The PSU delivers a stable +12V voltage which deflects no more than 2% from the nominal value, but the +5V and +3.3V voltages get close to the permissible limits: the former under maximum load and the latter under minimum load. On the other hand, the voltages are all within the required limits and do not deflect much under typical loads.

Output Voltage Ripple


The output voltage ripple at full load is within the permissible limits.


Enhance used to be fond of special fans in its power supplies such as fans with originally shaped blades or with 4-pin connection. Somewhat unexpectedly, the MODU87+ has a 140mm fan with the exclusive Twister Bearing but without any remarkable external traits.

Well, if you take a closer look, you will find the fan to be not so ordinary after all. It is connected with 3 wires, but that’s neither a standard 3-pin fan with tachometer output and nor a PWM-controlled fan.

The bottom limit for a fan’s voltage is determined by its control chip. The latter cannot work if the voltage is too low and the fan halts then. In PWM-controlled fans the chip is powered by 12 V while its speed is regulated by means of pulse width modulation at a frequency of 25 kHz via a separate wire.

Enermax came up with a different solution. On one hand, its fans are not PWM-controlled. And on the other hand, they have a broader speed range than classic 3-pin fans. The fan gets two supply voltages: the controller chip is powered by +12 volts whereas the voltage of the motor varies.

The table above lists conventional methods of connecting fans as compared with the Enermax fan. Easy to see, the main consequence of this discrepancy is that it is hard to find a replacement fan if the native one fails. Perhaps you can take an ordinary 3-pin fan and connect it to the “ground” and the second power pin (the one with varying voltage), leaving the tachometer output unconnected. And don’t forget to check out that the fan will be able to rotate at the bottom voltage.

When it comes to the EMG800EWT, its fan does not slow down to some record-breaking levels. Its bottom speed is 700 RPM. The PSU is very quiet, nearly silent, and remains quite comfortable acoustically even at full load when the fan accelerates to 1200 RPM.

The single downside I could spot was a weak but distinct electric noise I could hear from the PSU at zero load. On the other hand, there are no computers that consume 0 watts.

Efficiency and Power Factor

As promised by the manufacturer, the PSU’s efficiency is as high as 93% at the peak and only falls below 88% at very low loads when the PSU’s own power consumption in idle mode becomes important.

Standby Source

When the load was increased to 1 ampere, the standby voltage sagged alarmingly. However, it eventually stabilized at 4.9 volts, which is perfectly normal.


Enermax enjoys a good reputation and has not failed today, either. The MODU87+ can be recommended as a high-wattage, modern, stable and quiet power supply for gaming computers. It has only one downside. Its nonstandard fan may be hard to replace if you want to do that for some reason.

I want to emphasize the fact that the EMG800EWT is up to 93% efficient, which is the all-time record for power supplies ever tested in our labs. I have no doubt that the other brands will soon roll out their own 80+Plus Gold products, too.

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