So, in this case the two power supplies can give you as stable voltages as you can possibly get, but there are two considerable drawbacks. First, you must have the skills necessary to modify the PSUs on your own. Second, the most voracious components of a modern computer are supplied from the +12V source, so one of the units is going to bear a much higher load than the other.

Of course all these improvements and modifications are for hardcore enthusiasts because ordinary users would find it simpler (and even cheaper, considering the time spent) to buy a new, high-wattage power supply than to take the trouble of fitting two PSUs to their computers. And you have to think about where to put the second PSU in the system case, too! Well, the industry has already made a step towards the enthusiasts: the Cooler Master Stacker case has a place for a second power supply and an adapter for sending it a turn-on signal in parallel with the main PSU.

The same industry has involuntarily made another gift to people who’d like to use two power supplies. Every high-consumption component is now powered from the +12V source and the +12V power rail is split in several PSU outputs. As a result, the graphics card and processor have acquired their own external power connectors that are not electrically connected to each other (the CPU connector is located on the mainboard – it’s the well-known 4-pin ATX12V).

What does it mean? In old times when the ATX12V connector already existed, but PSUs had only one +12V rail, there was no reason why this connector shouldn’t be connected to the appropriate contact (the +12V yellow wire) of the mainboard’s main 20-pin connector. More contacts minimize resistance and power loss. However, this meant that if you tried to power the CPU from a separate power supply whose output voltage differed from the main PSU’s voltage (and they are never going to be exactly the same, of course), you got a short circuit through the mainboard with all the consequences.

The connectors had to be separated on the mainboard after the division of the PSU’s output lines had been made: it would be illogical to divide anything in the PSU only to join everything back together on the mainboard. So it has come to be that the 12-volt CPU power connector is not electrically connected to the 12-volt contacts of the mainboard itself. And you can apply different voltage to them, from different PSUs, without fearing any problems.

The same is true for graphics cards after they have acquired dedicated power connectors – first of the 4-pin HDD or floppy variety and then special 6-pin ones (and the power consumption of graphics cards has grown dramatically, too, up to 100 watts and higher).

And now the idea of using multiple power supplies has emerged again. On one hand, there appear graphics card models with dedicated power supplies. For example, the power connector of the ASUS EAX 1800XT TOP is placed on an external bracket and is connected to an external power supply. This solution helps unload the main power supply of the computer, but has two drawbacks. First, there are only a few graphics card models that come with an additional PSU. Second, if you use a SLI or CrossFire system, you have to power one of the cards from the main PSU or to put up with two additional PSUs.

The solution suggests itself: an additional 12V power supply that would connect to any graphics card and would easily support two graphics cards at once (or even four cards because Nvidia is actively promoting its quad SLI technology).

Two companies have come up with such products this spring. Thermaltake was the first with an official announcement, but FSP Group’s product was described in detail on the Web a few days earlier, although without yet being officially released. Anyway, we got a FSP VGA Power from Fortron/Source for out tests first.