Power all your fans and other added components only to the second PS. Keep all other system components on the first power supply.
Let me explain. There are some real problems with the methods shown and described in the example about the possibility of increasing system power. In the example provided above, there are only details for creating a method to turn both power supplies on nearly simultaneously, but not really how to take two 12v and 10A leads and make them provide 240w as described in the reasoning for this method. In their example, the power supply is used neither as parallel or series power supplies, but as two separate supplies which power every system component (which seems safest), but the total power from both power supplies is utilized by splitting devices onto both power supplies, which doesn't work for a single device requiring at least 120w with a 12v supply like the 120w peltier in their example, but does work for components requiring less power like fans.
There is a second problem with their example. There seems to be implied a concept that using two power supplies for separate system components is ok, which in my opinion is not a good practice.
Running a mother board on one PS and some HD/CD/DVD-ROMS on the other may and probably will cause problems because this effectively allows the 5v and 12v supplies from the molex connectors on one PS to return on another PS through the motherboard via the IDE ribbon cables (yes, this seems possible even though the great majority of current and voltage returns via the molex ground -- in other words, the positive level on one PS returns to negative on another PS. This is definatly not good in the long term for system components like the motherboard, HD, DVD-ROM, CPU, RAM, PS etc). This is more important if each PS is a different model and built differently with different specs, with different current regulators, but is still important to note that PS are not likely to be engineered to carry twice the current or twice the voltage of their specifications nor are they designed for half the impedance via changes by implementing parallel circuits.
Running all system components on one PS while running all added lights, fans, peltiers, pumps, panel LCD's and all other user added gadgets to the second PS is the only right and safe way to preserve the life of your mainboard, CPU, and all other components.
For example, using two power supplies doesn't double the voltage levels unless used in series (like two batteries with negative to positive to negative poles [ie, like 2 batteries in a flashlight at 1.5v each making 3v totoal - / + / - / + ]. In the same type of series setup, current isn't additive, but remains the same for each power supply and the output levels on the PS (and aren't we glad for that).
So if one PS is 10A and the second is 10A and two separate voltages of 12v on each are in series, you get 10A at 24v which is 240w, but the voltage of 24v is too high for the components. (Having a different PS supply a HD/CD/DVD permits somes of the voltage to return to the other PS which may cause an elevated or decreased voltage level, not to mention problems with current, problems with PS regulation and problems for other system components. This is how to blow up your components.) With regular electical outlets, you would never take + from a wall jack on one circuit in a house and connect it to the - on another circuit to power home appliances (I wonder if there is some reason why they don't make extension cords that do this? This would of course, cause a ground fault.)
Most electrical/electonic units require power with specific voltage and current requirements and the units to be powered also demonstrate less tolerance to moderate voltage fluctuation. Current draw is usually limited by the powered units which makes it possible for units to have significantly more current available as a ratio of needed/supplied current (%) than compared to voltage ratios with much lower variance ratios.
In parallel, two PS of 12v each will present power that is still 12v, but the current will be additive. This is how the current increases from 10A + 10A = 20A (like 2 batteries side by side with both negative terminals connected to a circuit and both positive terminals connected to another circuit.) But connecting two PS that are not designed for this type of connection is dangerous and not recommended, so using the techniques to install a second PS to balance more of the load is reasonable, but doesn't mean you can now install a different CPU/heatsink that requires a 450W PS (where you still get 12v at 10A except from two sources).
Overall, there is nothing wrong with the example since they don't show PS lines connected togther except for the relay switching inputs, and this is the safest way to use multiple power supplies. It's just the way the power is referred to is incorrect as though the user will now have 12v at 20A (or 240w), which is totally incorrect. Each PS may supply 250w (or 250W + 250W), but the total power although additive in concept is not really additive in either current or voltages supplied, but only in total cumulative power supplied by both PS to all components.
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