I want to build an auto-feeder with the RCX 2.0 for my cat. The problem is, that I often had to exchange the batteries. Is there an adapter for the RCX to connect it to a power point?
The older RCX 1.0 had a power plug inbuilt. However Philo has shown how to create one yourself in a fairly simple way: LEGO® 9V Technic Motors compared characteristics, scroll down to the section "Getting maximum mechanical power from RCX output" towards the bottom of the page.
The idea is to create two fake batteries and draw a wire from each, creating a +9V and a ground from a separate source. You would need a voltage regulator though. WARNING: supplying incorrect voltage can destroy your RCX.
Image and technique by Philippe "Philo" Hurbain © 2000-2009, used in accordance to "You are free to use it for any purpose, just give me credit...".
If you'd rather not cut off the ends off two batteries and jury-rig in rods of hot melting glue to act as spacers, and instead have access to a 3D printer, take a look at http://www.thingiverse.com/thing:122810 :-)