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Second power supply but not computer specific, will it work?

Last response: in Components
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January 17, 2012 10:13:38 PM

Hello,

Firstly I will start with my situation :

Have a 4 year old pc running off a 460W PSU and wanted to upgrade the existing graphics card (gigabyte 8400gs) to a asus 9600gt (cheap at $48 USD - seccond hand), thinking the 460W PSU should still be plenty to power it, which as it tuns out apparently it can't ( insufficient power supply to gpu message upon entering the welcome screen after booting).

I have connected the PCIe 6pin connector to it from the psu and also tried using the 2 molex to 6pin converter with to apparent difference.

I have measured the voltages of the free molex connectors and also the PCIe 6pin connector, all read 12.01V-12.03V.

Is interesting to note that without any external power connector (just the PCIe slot power) no warning message appears (I know it uses around 10W less power according to a power meter), as a side question, any idea what that is about?
Now my main question is:

Can I connect a 12V power supply, which is not a computer specific one (used for powering amateur radio devices among other things) to the 6pin input on the graphics card to supply the additional power required?

Wanting to do this basically because I dont have a second PSU to connect to it which I know works as on the sticker and dont want to buy another PSU not knowing if the problem lies with the GPU.

Some additional information

Existing PSU : PowerMan IP-P460Q3-2 (suspect it could be a cheap one, compounded with it being 4 years old and subsequently not supplying the specified power (460W)
Mainboard : Gigabyte G1975X
Processor : Intel Pentium D (XE) 930 @ 3000 MHz (seems to permanently be at about 3.1GHz)
RAM : 2 sticks each 1gb and 2 sticks 512mb each
Hard Disk : ST360015A (60 GB) ( 6 years old - still works fine though but yes could be a lot better :p )

Had a externally powered external HD, 2 disk drives and a floppy connected but disconnected them to see if it made a difference (it didn't effect the GPU but according to a cheap power meter which i plug the computer into it shaved around 6W off)

If anybody could share their thoughts it would be greatly appreciated, thank you :) 
January 17, 2012 10:36:06 PM

I was thinking along those lines and have seen that review though im not sure if it makes any difference functionally (ie not the same psu) - the psu casing is the old computer gray color, no blue led fan and different colored connectors, perhaps its just a different version as such otherwise something fishy is going on.
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January 17, 2012 11:42:35 PM

oh now this is very weird...with the 6 pin connected the cpu i believe is effected (on a non graphically challenging thing it loads slowly (web browser) however without any external power plug connected it doesn't and in COD4 (only game i have on on hand to benchmark this... same settings from when i used the 8400gs..20-40-ish fps to 90-120 fps (no power warning on startup with external power disconnected?)

GPU is maxing out at around 54C (not a very demanding game though at min settings)

I did connect a molex to the 12V connecter on my motherboard, which in the manual said it supplied extra power to expansion slots in case of sli..so not sure how this would help a single gpu and 75W is still the max through one expansion slot?
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