http://www.newegg.com/Product/ProductList....Submit=Property

What motivation would I have to spend the extra $16 for a TPII-480 compared to an SP-500? What's the real difference?

(Information from Antec's site)
Both have dual 12v rails.
The SP has PCIe power connectors but the TP doesn't.
Input current for the SP is 10A (vs 12A) at 115V DC.
The output (amps for each voltage) is close to the same.

I'm not seeing any major difference. Did I miss something?

EDIT: These are the lowest prices I could find including shipping:
SP-500: $66
TPII-480: $74

if you looked on antec's site and not newegg, the differences are obvious...

the truepower is better because of tighter tolerances
also the truepower has pci-e because it's an atx 2.01 psu

look on the manufacturer's site for info, not retailers

http://www.antec.com/specs/SP500_spe.html
http://www.antec.com/specs/TPII480_spe.html

You got me with the tolerances. But is the difference between 5% and 3% really worth it?

If you want the best. Then yes.

i bought my psu (neopower) because it is based on the truepower, but is also modular...

Besides the load percentage tolerances, the True Power PSU's have dedicated circuitry for the 3.3v rail (not a huge factor, but unique). Traditionally the 3.3v line is derived from the 5v line, so the combined load of both the 3.3v and 5v lines would be lesser compared to dedicated voltage lines. However most PC's dont draw a lot of amps from either the 3.3v or 5v line. More emphasis is placed on the 12v lines since CPU's/GPU's are drawing most of their power from there. As for a decision between the two, either one will power most computer setups with room to spare except maybe a SLI/crossfire setup.