USB 2.0 Combo drive vs. Powered USB 2.0 Combo drive

[staeiou]

I'm looking at X41's, and I have the option to add a USB CD-ROM drive. Of all the options, there is a "ThinkPlus Powered USB 2.0 Port CD-RW/DVD-ROM Drive [$195.30]" and a "ThinkPlus USB 2.0 CD-RW/DVD-ROM Drive [$139.30]." Obviously, I want to spend as little money as I can, but can anyone who has bought either of them comment on the differences?

Most importantly, does it require a AC adaptor to connect to the laptop?

[bollar]

I have the USB 2.0 Portable Multi-Burner Part 22P9175.

It comes with a power adapter, but with an X41, it has a special cable that allows it to get power from the second powered USB port on that machine, eliminating the need to use the adapter.

[JimMorris]

This should help clear up "powered USB" :

www.usbpluspower.org

[Yotam]

Is IBM/lenovo the only which produce laptops and accessories with powered usb port/connection? I can't find any other cd-rw with this connection.
Does anyone know if "regular" USB cd-rw/combo drives need to be connected to AC power adaptor in order to work?