PowerColor had it's AGP card in the new Radeon HD family on display at it stands and there seems to be a crucial difference between the two cards, the 2600 Pro has an PCIe power connector.
The Radeon HD 2400 Pro has a standard 4-pin Molex connector, so no problem to get this one working with your current power supply in an AGP system.
However, DAAMIT seed fit to put a PCIe power connector on the HD 2600 Pro AGP version, which doesn't make a whole lot of sense, unless it means that a single Molex connector can't deliver enough power, but that doesn't seem very likely.
This means that anyone with an older power supply needs to use an adaptor to get this card working in their system.
This is what the final cards looks like: