Can i use external PSU for my GPU


I got an old pc following are the specifications

Dell Optiplex 755
4gb ddr2 ram
300watt built in psu

I have got another PSU ( Cooler masterExtreme Power Plus 500W )

Note : I used this power supply to run my r9 270x on another pc, which i am currently using for mining. I want to buy another r9 280x or r9 290x and connect the power supply 6pin connectors to the gpu but in the old system i.e ( Dell Optiplex).

I am currently running 1x r9 270x + 1x r9 290 on my mining rig with corsair TX850 smoothly. I just wanted to know if its possible to to buy a new card as mentioned above and connect the external 500watt psu only to the card but not to the motherboard ?? as the motherboard and other parts of the computer will run on the builtin psu which is 300watt.
6 answers Last reply Best Answer
More about external psu gpu
  1. yes it is possible, you will need a dual PSU adapter to turn on the other power supply.
    NOTE This can occasionally cause issues as you are using 2 different earth points in the one PC (one earth from each PSU)
    most of the time this has no effect on the system however

  2. my best recommendation would be to transplant that PC into a new case that would allow for a better PSU.
  3. The system cannot be customized that is why i wanted to know if i can add external psu. i saw the dual psu adaptor. As far as i could understand that i connect both psu 24/20 pin to the adaptor and then connect the other side to the motherboard ?? my country does not support ebay and i dont think the dual psu adaptor would be available here. Anything you would recommend me that can workout manually ?? Thanks alot for quick response :)
  4. Best answer
    nothing that would be safe or easy to use.
    the motherboard needs to send the signal to the PSU to turn on and off when you push the switch.

    you still should be able to remove all the hardware from the dell case and put it inside a normal PC case that will accommodate your bigger PSU
  5. Thank you very much :)
  6. There are ways to power a GPU with an external PSU if you own another PSU here's a few steps

    (1) Get a paper clip or any medal wire not a plastic covered paper clip

    (2) Connect the Green neutral wire to any of the Black ground wires on the 20 - 24 pin connector not the molex or sata power cables.

    (3) Connect the GPU to the PSU either by a adapter or the one built in the PSU

    (4) **Important** Power the GPU first then power the computer

    The reason why step 4 is really important is because whats going to happen if you power your computer first,
    its going to give you a black screen and this is because the GPU is verifying its getting the extra power by the PSU if it isn't doesn't its not going to respond the POST and its going to switch to onboard graphics which is slow and unreliable.

    When you power the GPU first then power the computer its going to magically work

    **Warning** Don't power the GPU when you have your computer off or in sleep / hibernate mode. the reason why is because the GPU is still getting power and the processor inside is going to output heat and when the computer is asleep or off the fan is off and this can overheat or even destroy the GPU.

    Tips: when you put your computer to sleep and your GPU isn't receiving power because you turned it off, power the GPU then wake up the computer. if you don't do that your computer isn't going to see the GPU then switch to onboard graphics.

    This is the cheap method its not going to look nice but its most likely going to work.
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