Max,
PowerBox and Power Expander are trade names for roughly the same device. Here are some links below and suggestions that you can use depending on your setup.
Castle BEC Pro:
CC BEC PRO 20A MAX OUTPUT, 12S (50.4 VOLTS) MAX INPUT SWITCHING REGULATOR
Pro: Lowest cost alternative. Good, regulated power, redundancy.
Con: It uses 2 channels on your receiver. So, if you need all nine channels or if all 8 servos need 8 channels, this will not work for you unless you use some creative wiring and lots of Y cords.
Smarty-Fly Power Expander **this is my system of choice***
PowerExpanders
Pro: Higher end units allow you to have a failsafe for your ignition attached. Dual power supplies, dual power inputs. Bat sharing.
Con: A bit tricky to set up as the instructions could be better
PowerBox Regulator -only-
Parallel Regulator Sensor, from PowerBox Systems, pbs-6310 - Chief Aircraft Inc.
Pro: A bit more refined solution than just the BEC Pro. It has dual power inputs, failover. Nice switch interface.
Full PowerBox system
Evolution, with Sensor Switch and Patch Cables, from PowerBox Systems, pbs-4230 - Chief Aircraft Inc.
Pro: The Cadillac of airplane power systems. Does everything you can think of.
Con: $$, but what did you spend on the airframe and engine??
