A Displacement current is a high voltage discharge current. When the Asuran Dr. Elizabeth Weir was trapped in subspace due to digital ascension she interfaced with Lt. Colonel John Sheppard's team's Puddle Jumper when she located it. This interface caused power spikes and anomalies making the team lose control of the jumper. Another side affect of this was the discharge of high voltage displacement currents around the jumper. The same thing happened when she, and later when the other Asurans, interfaced with Atlantis' systems causing discharges of displacement currents throughout Atlantis. When the other Asurans entered the system it eventually caused the death of at least one person on Atlantis. (SGA: "Ghost in the Machine")