^ No, mATX spec powersupplies use ATX connecitons, but are physically smaller. They use the same width, height, and mount points as ATX ones, but are shorter in depth. Some OEM cases, like HP's old Pavilion line, used these. Normally it's all ATX though.
Oddly enough, the old Pavilion towers had full ATX motherboards.
I'll post a pic of them side by side in a minute...my phone takes a bit to upload since there's no 3G here.