The Black Art of Dual PSUs in Your Enthusiast PC

Putting two powers supplies in your computer has been a recurring subject in our forums for years. While the physical process of making that happen is not exactly rocket science, it still can be daunting for some users. Today we show you a few products that make it easy for anyone to double up on the power should your wattage needs increase.



In today’s tongue-in-cheek entitled The Black Art of Dual PSUs in Your Enthusiast PC, we have covered a range of different products and the applications. These have ranged from the very cheap to the very expensive but all of these will, after a fashion, allow a user to run more than one power supply at one time without modifying this configuration themselves. There is, of course, nothing wrong with DIYing it if you have the tools and supplies, which are minimal, but as we discuss today there are times and places where this approach is not practical. For users looking for a how-to on these kinds of mods there are a plethora of resources available on the web and we do not have anything to add in that respect. However, the conclusions and thoughts on some of the products, and other methods, for running two power supplies at once provided here covers the commercial products that may be jockeying for your buying dollars if you so choose to go down the dual power supply path.


The first product we looked at today was a new item from DLL Industries, the Add2Psu adapter. The actual adapter itself is a single PCB with a female Molex connector, female 24-pin ATX connector, and a relay on one side along with a piece of sticky tape for mounting on the other. It is very cleanly manufactured, but then again it is also an extremely simple product for a manufacturer to produce so it really should be well done. In actual use, we had no problems with the product and it worked completely as advertised. Indeed, between this product and the Lian Li Secondary Power Supply Starter Kit this is probably the better of the two, and certainly the better of the two if you want to run three or more power supplies. The Add2Psu adapter also gives you the ability to mount the adapter wherever in your case you would like, which is nice as this will help in your wire management. Particularly because wire management will likely be a bear if you have two inexpensive power supplies in your case. The two, at least academic, downsides to this product are: 1) for each Add2Psu adapter you use you will lose the use of one Molex connector, and 2) the potential longevity of the sticky tape in keeping the product mounted in a hot case. In reality, these may not be issues for everyone as the number of peripherals using Molex connectors is waning and you can always reapply new sticky tape or use another non-conductive means of attachment for the product. All in all, the Add2Psu seems to be a solid product for what it is and can be found for $19.95.

Lian Li Secondary Power Supply Starter Kit

The second product we looked at today was the Lian Li Secondary Power Supply Starter Kit. This particular product took a slightly different approach to the same task of running two power supplies at once as the Add2Psu adapter. With the Lian Li Secondary Power Supply Starter Kit we get an adapter cable that passes the PS_On signal from the first power supply to the second power supply by combining the two 24pin ATX connectors. The name "Kit" for this product by Lian Li was probably a bit misleading as all that comes with the "Kit" is the cable. The cable itself, however, is well constructed as well and, again, like with the Add2Psu there is no reason it should not be as it is a very simple item for a manufacturer to produce. The Lian Li Secondary Power Supply Starter Kit has two additional features. The first, is that the cable itself provides an extra ~4.5" of reach so if you are in need of a slightly longer 24-pin ATX cable in your system it provides that extra reach just like a regular extension cable. The second, is that unlike the Add2Psu adapter, the Lian Li Secondary Power Supply Starter Kit does not use a Molex connector to operate that could be used for something else; rather it used the 24-pin ATX connector on your second power supply which would have been hanging free anyway. On the downsides here, if you want to run three power supplies (for some reason) you are going to have to daisy chain the 24-pin ATX connectors which is going to increase your connection points, resistance, and cable stiffness as well as make wire management not nearly as nice and neat as was the case with the Add2Psu adapter (even when running just 2 power supplies). As with the Add2Psu adapter, the Lian Li Secondary Power Supply Starter Kit seems to be a solid product for what it is and can be found for $14.99.

Auxiliary Power Supply (FSP Booster X5 450W)

Whereas the Add2Psu and Lian Li Secondary Power Supply Starter Kit were only pieces to the dual power supply puzzle, an auxiliary power supply such as the FSP Booster X5 450W is the complete package. The FSP Booster X5 450W comes with not only the means to turn on a second power supply, but also the second power supply which fits in a 5.25" drive bay. The biggest problem with this type of setup is it is directly tied to the quality of the power supply included (see the ePower JuiceBox 450W power supply we reviewed previously), unlike with the Add2Psu or the Lian Li Secondary Power Supply Starter Kit, which can blame any power problems on the quality of the power supplies they are connecting. The actual quality of the FSP Booster X5 450W will be examined more in depth in the actual review of that product later. Now similar to the Add2Psu solution, the FSP Booster X5 450W uses a Molex connector along with a relay to synchronize turning on both power supplies at the same time. As such, with this setup users lose a Molex connector in the process. Unlike with the Add2Psu adapter, the FSP Booster X5 450W lacks any extra Molex connectors (being an auxiliary power supply) so no matter what you do with this solution to the dual power supply setup you are going to be down a Molex connector and only gain more PCI-Express connectors. One of the other, or perhaps the biggest, benefit to the FSP Booster X5 450W, or any auxiliary power supply, is the form factor. For users who lack the room to mount a full sized ATX12v power supply, the ability to mount the FSP Booster X5 450W in a 5.25" drive bay gives this product a useful range that outpaces the other solutions presented. The price on this particular 450W FSP unit is $79.99 after MIR.

Redundant Power Supply (Athena Atlas 800)

The final product we looked at, and just briefly, was the Athena Atlas 800, 800 watt power supply. While this particular product is a dual power supply setup under a relaxed definition of the phrase for today’s article, it does address the one big shortcoming of all of the previous setups. Redundancy. All of the solutions previously presented result in running two power supplies in tandem but provide no fault tolerance, whereas the Atlas 800 provides just that. If one module in the Atlas 800 fails, the redundant module can continue to power the system (though with the alarm sounding). For most users this kind of configuration is overkill, and rather specific. Indeed, the Atlas 800 has a limited number of connectors when compared to other 800W solutions, or even a low end dual power supply configuration using the Add2Psu or Lian Li Secondary Power Supply Starter Kit (unless users choose to use some really bad power supplies), but this issue as well as capacity has been improving with this type of product from the enthusiasts perspective. However, for its intended application and bulletproof-ness nothing else looked at today can come close to touching this product. Quite simply, if a single power supply in any of the other setups fail then, well, we go from a 800 watts worth of power to just 400 watts of power, unless it is the main power supply and then we are left with no functional system. If the Atlas 800 loses a module, we go from 800W of power to 800W of power, and an alarm going off. As with the FSP Booster X5 450W and the auxiliary power supply idea, the actual quality of this particular unit will be more thoroughly examined when we post our full review of this unit. Also like with the auxiliary power supply component, prices on this kind of setup vary widely and these can be quite expensive but if you truly need one, your system's data and up-time is likely worth far more than the cost of a quality redundant unit.

Paul's Thoughts:

I will just start this off by saying, I think the idea of running two power supplies at once is an idea whose time has generally come and gone. I won’t deny that at one point in time the idea certainly had significant legs. However, with the proliferation of quality higher powered power supplies, and the general drop in those prices, the wind has kind of been taken out of the sails here except for in limited situations. For instance, we have reviewed products that hit very close to the limit of what is practically possible in North America in terms of usable PSUs when we reviewed the Ultra X3 1600W and the SilverStone Strider 1500W. While these two are the extreme end of the spectrum the availability at prices below ~$400 does take a lot of the argument about the ability to get high capacity any other way than with a dual power supply setup or any other way that is prohibitively expensive in a single unit. Further complicating this is that quality 1000W power supplies are available for $100 to 150 at e-tailers such as Newegg, Amazon, TigerDirect, Directron, etc. on a rather regular basis and these capacity units are MUCH more accurately sized for the VAST majority of even high-end enthusiast systems. To match, or best the value of these quality 1000W units, users would have to find a pair of quality 500W power supplies and either the Add2Psu or Lian Li Secondary Power Supply Starter Kit for $100, or less, which means you have a budget of about $40 per power supply. I tried doing this at retail, and yes retail is not e-tail I know, and the closest I could get was two 400W supplies.

At the time of the writing of this review I also price shopped this type of setup on Amazon, and Newegg, and I was able to just barely hit the necessary price point (sale prices of course will always affect these results on both the 500W and 1000W units). This price shopping also lead to a, somewhat, surprising result when I looked at the FSP Booster X5 450W through these same lenses. I will fully admit I had assumed the reason the why the auxiliary power supply market seemed to be shriveling up was price. However, when I actually looked at it in the context of this topic today I believe I was wrong. At the time I purchased the FSP Booster X5 450W it was $89.99 ($79.99 with rebate). Looking online at quality 450W power supplies the cheapest regular priced 450W power supplies I found were in the $40-50 range. That said, after buying a 450W power supply to supplement your current one and either the Add2Psu or Lian Li Secondary Power Supply Starter Kit you are looking at $60 to $70. Additionally, this is unlikely to net you four PCI-Express connectors with your 450W power supply like the FSP Booster X5 450W would and typically powering video cards is what users are looking at these days when they need more power. With that considered, the price of the FSP Booster X5 450W is not really out of line with the other dual power supply setups since you get more PCI-Express connectors and it is significantly smaller. The problem is though, you are still looking at the same price overall as a quality 1000W power supply once you get your base power supply and auxiliary power supply . In the end to really save money going with the dual power supply approach you are most likely going to have to go with two very cheap (and likely questionable) power supplies or score a very sweet deal. Any way you slice it, two cheap power supplies are still two cheap power supplies, and you would be better off buying a single good power supply. Unless you are absolutely space restricted in a small form factor case and need more power than a replacement unit will provide, then you may want to look towards the auxiliary route which is surprisingly viable in limited situations.

The Bottom Line

Often here at [H]ardOCP we deal in niches, and this is particularly true when we look at dual power supply configurations today. None of the products we looked at today are in and of itself a bad product, rather these all are nicely done and function well. They are all, however, limited application products even for enthusiasts and that truly defines this issue; particularly when many users can accomplish what the Add2Psu and Lian Li Secondary Power Supply Starter Kit do without buying a ready-made product. In that very narrow window of applications, these products can make sense for a user if you are starting from scratch and you do not have the materials already on hand to do the mod to turn on two power supplies at once in a lasting way. The reason being, by the time you buy the pins, pin tool, wire strippers/crimpers (or just use needle nose pliers), Single Pole Single Throw switch, relays, or wire then have all of it shipped to you, you are going to end up likely beyond the same price point as the Add2Psu adapter or the Lian Li Secondary Power Supply Starter Kit as both products are relatively cheap at $14.99 (Lian Li Secondary Power Supply Starter Kit) and $19.95 (Add2Psu). From that perspective, these products are useful and the price premium on them is not as much as it seems at first blush.

When it comes to the auxiliary power supply, we already know that not all of those options are good, (i.e. ePower JuiceBox 450W) but if the FSP Booster X5 450W passes our load testing, its price premium also would not be as out of line as it might appear at first look. Lastly, the Athena Atlas 800 redundant power supply is a whole different ball game, with a whole different set of parameters affecting its value, and users are encouraged to check back when we post its review in a couple of weeks.

The Add2Psu and Lian Li Secondary Power Supply Starter Kit are both very solid products that go about solving the same problem in different ways and are very likely worth the affordable prices asked, if you know that doubling down on power supplies is the right answer for you.