It actually isn't too technically difficult to do what he wants to do. What I like to do with old AT supplies is run the 5V from three similar units in series to step the voltage up to 15V, and be able to then take advantage of the high output current available off this line. It requires a very easily made modification to two of the supplies. The problem with answering these questions (and I expect from how many times it has been asked on the forum that it will be often repeated) is simply that you have no idea whatsovever what is really going through some of their heads, or even if they can solder or understand basic electronic theory. I have seen so many mistakes made by novices that I feel it's just not healthy to encourage them. This forum might get blamed too, which is why if they insist on doing it I don't mind steering them in the right direction...through email, not here, knowing that they will probably make a mistake and fail the "smoke test". Switching type supplies, in particular the older units, usually have a requirement for a minimum load on their output terminals. Typically it's in the range of 2 to 4 amps on the +5 volt output and from 0 to 2 amps on the 12 volt output. Some supplies require this minimum load on the +5 volts only. To achieve proper regulation you can use a low value/high wattage resistor (it wastes power, but you do what you got to do). The simple cure for wiring them in parallel involes using blocking diodes on the +output leads to protect the supplies from each other. This will drop the output voltage by the theoretical 0.7V (but in the real world is more like 0.6V). If you have adjustments internal to the supply you can compenstate, if not, you can perform a more technical operation...and so on. If the supply has an orange "power good" wire, depending on the application you would tie this into the +5V line. Bottom line for the person who has to ask these questions is that you're fooling with something unfamiliar and you're likely to get bit. Be Carefull, be safe!

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well, no offence and all in any way, but I really dont ask how to connect two PS to the system, all I ask is how can I turn on/off second PS together with system PS. or it has to be goin through process of paralleing both PS together? if so, then I'll stick with installing seporate switch for second PS. (btw, this PS doesnt have power switch at all, so I've got to pull out power cord. 8*( P.S. does PS takes any electrysity if it's in stand by? I mean, it powered on, but nothing is connected to it. in old times it was sucking some (very little) power, does it do same now? P.P.S. thx for replying, now I learnd something I didnt know before. man, time is changed alot! lol remmember having my 48kb RAM ZX Spectrum (3.5 MHZ) witch had power supply that will make the comp freeze or reboot after u turn light switch on/off...hehe

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V@no, Your right, I'm sorry for the digression but think it needed to be said. No, you won't have to parallel all the lines of your two supplies in order to control the on/off of both from a single switch. Yes, it does take electricity even if it is standby. At least this is true for the ATX supplies. The ATX supply is controlled by the motherboard, which has +5V being supplied to it even when the computer has been turned off (thats how things like wake-on-lan are controlled.....and it also takes care of keeping the CMOS memory refreshed so you're not draining the battery). When you press your power on switch you are really grounding a +5V logic ciruit on the motherboard. The motherboard then grounds the "green" wire to your supply, which then attempts to turn on the power supply (note that in your original post you were taking this wire to a negative 12 volts, rather than ground). At this point you still may not be able to get an output from the supply due to a several reasons...reasons that may make this post way too long. I still am not sure what type of arrangement you have. Are both supplies ATX? If you are uncertain go here; http://www.bigedtech.com/articles/145.php Most switching power supplies have the ability to "Power Share". If the +5V line (or, node...for the purists) is only lightly loaded, the supply will be able to exceed the rated value on another line, such as for your purposes the +12V. There is a good deal of room to wiggle here, but if you push too far you can exceed the power limitations of the actual components in the supply and damage something. Tally up the wattage your fans will draw. If you need further assistance then please feel free to email me, as I shall likely not post another comment in this thread. good luck

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