The Power Source is a quest item in Act III. It is needed to power up the Dwarven Automaton at the gate in
the Imperial Camp, which will then open the door to the Clockwork Core. Professor Stoker sends you on the quest Some Assembly Required to retrieve it from the Scrapworks at the end of the Middenmine, but it turns out that it is drained. To recharge it, you will need to gain access to the Emberworks.