Power nodes are seen in both TimeSplitters 2 and TimeSplitters Future Perfect. In TimeSplitters 2, they are seen in the Robot Factory. Depending on which difficulty level you are doing, there will be around four or five. In TimeSplitters Future Perfect, there are three in the Something To Crow About level.
In both of these levels, an ElectroTool is the only way to destroy them. The ElectroTool feeds energy into the node, thus making it explode due to all that power quelling inside the base of it.