I took a quick sprint over to Soyata (practically walking distance) and bought a power supply. What a pain this has been. But when I got back in my car to drive home, "Everywhere" by Michelle Branch was playing on the radio, so at least that gave me something to smile about.
The power supply they gave me, while P4-approved, is only 300W. So I'll probably swap it for the 350 when that comes in like 4 months or however long it'll take.