Looks like that moddiy adapter should do the trick. I like the rest of you bought an Acer with the 12 pin power supply connector, and I found this thread very helpful. After attempting some staple pin removal tricks, I actually ended up making a pin remover myself similar to the original Molex pin remover as I found regular staples too flimsy. I had a Corsair 650 Watt PS with very tricky pins to remove. I used some images of a regular 20/24 pin ATX power supply pin diagram along with the 12 pin Acer style PS pinout diagram to compare to.
It helps to draw out the 12 pin diagram (H1 in the eBay image) and write the names of what goes where next to it (+12V, COM, etc) plus reference the wire colours as then it becomes simple unplug and plug.
Swapping out the pins wasn't too difficult, but you really need a good pin removal tool or method as it can be frustrating. I ended up soldering a jumper pin to use between 2 and 3. You have to be careful where you solder the wire onto as the pin has two parallel metal guiding fins that slide into slots in the connector, and there isn't much room in there to get the pin to fully seat with the jumper soldered on. I used a pin from a dead power supply.
I then was able to install my Gigabyte Radeon R9 270 video card. That was a bit of a trick itself as Windows 8.1 shows a blank screen for the longest time. I didn't think it was working the first few tries, and after doing a few things like adjusting BIOS settings it still didn't work. I even flashed the BIOS to version A4 which didn't seem to do much, and I also tried installing the video card drivers without the card in (which resulted in some errors). What worked in the end was that I left it to boot with blank screens (I have two monitors attached with DVI cables), and Windows 8.1 eventually installed the driver and boom the monitors activated on their own. I had to leave it for some time though. I then was able to install the current drivers on and get everything adjusted to my liking.
So for those in the same boat, keep the faith, your Acer does pose some challenges in the way, but they can be worked around. I think that $19 adapter doesn't sound too bad as then you can swap out PS's much easier and quicker without needing to swap pins out.
Sorry for bumping an old thread but I have another question regarding this situation.
I have a Gateway DX4885-UR1B. I finally decided to swap out the 300W PSU with a Thermaltake 750W PSU (TR2 RX-750AH3CH) from an old unused PC. As we speak, I just bought the moddiy.com 24 pin to 12 pin adapter.
My question is aside from the 4 pin and the 12 pin connection, is there anything else I need to do? In my old computer, the Thermaltake PSU has dedicated PCI-Express cables connecting directly to the graphics card but I don't see any that is needed for the GTX645 in the Gateway. Also in the old PC, the SATA connectors were used as well but it seems like the SATA power is drawn from the motherboard in the Gateway. So does that mean all the extra cables are essentially useless now?
I just want to make sure everything is copacetic before I put everything back together and turn on the computer.