It's square, nonstandard, and you'd have to get a replacement from Apple.
And for the record I don't think this is a big deal at all. I mean how often do you lose power cords? And what ever could damage your power cord would completely hork your mac anyway.
Being a stereotypical Mac user, I never look at the female end, but now that you bring it to my attention, I should probably check to see if it's any different from the one on the back of my G5.
Lemme just pull the cord out and have a look at it here and see if its any diffe...
Take note that the new PowerMacs also have twin Gigabit Ethernet ports (with Jumbo-frame support), now support workstation-level graphics cards, and ECC RAM. I suspect they looked over everything on the box to upgrade it to "workstation-class" toughness.