Lately, Acer and Gateway computers both started selling desktop models with proprietary 12-pin PSU-to-mobo connectors instead of the standard ATX 24-pin or 20-pin connector. This makes it extremely difficult to replace the PSU or the motherboard. You will have to send the whole computer back to the company if you need either of these parts replaced, or find an authorized seller of the specific Acer/Gateway part numbers. Thus far I have only found 1 place on the entire web that sells replacement PSU's and I searched the web for days. Not even eBay has them.
Also, upgrading the PSU to anything higher than the original 300 watt PSU is impossible since they didn't make any model larger than 300 watts. What makes that important is that if you had dreams of upgrading to a decent dedicated video card - you are out of luck.
These specific models of Acer / Gateway desktops utilize the proprietary 12-pin power connector:
Acer Aspire AT3-605-UR20 . (i5-4330 / 12gb / 2tb)
Acer Aspire AT3-605-UR21 . (i7-4770 / 12gb / 1tb)
Acer Predator AG3-605-UR24 . (i7-4770 / 12gb / 1tb)
Gateway DX4885-UB3A . (i5-4430 / 8gb / 1tb)
Gateway DX-4885-UR21 .(i5-4430 / 8gb / 1tb)
This model may also use the 12-pin power connector as well:
Gateway DX4870-UB318 . (i5-3330 / 8gb / 1tb)