Just call it a power cable and you'll be good.
Age and specs really determine the value of a Mac. Macs with low specs built in the early 2000s aren't worth much at all. The G4 350 PCI I have here at work probably draws more in electricity than it's worth each month.
Then too, exapandability is also a factor. The G4 450 AGP stitting right next to the G4 350 PCI at work is considerably more expandable than the 350. The 450 has low specs but because you can upgrade it, it's value is probably higher.
Generally though PowerPC Macs produced around 2004-2006 have more value because they have higher specs and are younger.