Powerlinx

A Powerlinx symbol from Energon. Energon Transformers with same-colored Powerlinx symbols can combine with each other. (Ironically, Transformers with a red Powerlinx symbol, as depicted here, are the exception to this rule.)

The term powerlinx has several different meanings, most of which have to do with robots combining with one another. In the Armada franchise, powerlinxing was the act by which a Mini-Con attached to a Bulk, adding a boost of extra power to the larger robot.

In the Energon franchise, powerlinxing was the process by which two similarly sized Autobots combined (via the Spark of Combination) into a single, more powerful robot.

Cyber Planet Keys do not Powerlinx. Well, except Demolishor's. And deluxe Optimus Prime's.

Toys

Armada

In the Armada toyline, Mini-Cons had Powerlinx ports—small, circular recesses with single plastic pins at their centers—that could plug into appropriate Powerlinx hardpoints on the larger Transformers figures. All of the Armada toys, Deluxe class and upwards, had at least one "active" hardpoint that, when a Mini-Con figure was attached, would activate some kind of gimmick. The majority of other Powerlinx ports on figures were "dead"—sculpted details not linked to any gimmick, simply there for attaching Mini-Cons. Some of the larger toys, such as Super Base Optimus Prime, Gigacon Megatron/Galvatron and Unicron had several active Powerlinx ports linked to different gimmicks.

Energon

In the Energon toyline, Powerlinx was no longer associated with Mini-Cons and larger robots linking together, but with the Autobots (Combat/Deluxe class and upwards) combining with each other or combining with some auxiliary drones that were packaged with them to create larger robot toys. Combat/Deluxe and Mega Combat/Voyager class Autobot toys could combine with each other, Commanders/Ultra class Autobots could only combine with whatever auxiliary unit was included in their package, while the the Leader class Optimus Prime could combine with his included Prime Force drones, the Mega Combat class Wing Saber and the Supreme class Omega Supreme.