From The TimeSplitters Wiki

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 4 or 5. In Future Perfect, there is 3 in the Something To Crow About level. In both of these levels, an Electrotool is the only way to destroy them.