To measure power converter leakage to ground, power up the converter with no ground connections, either on the case or AC cord. Then simply measure the current between one side of the AC line and the converter ground connection, then repeat for the other side of the AC line. The measurement can vary with the load on the converter and the AC input voltage. As I mentioned earlier, it's hopefully pretty balanced to avoid GFCI trips. A legitimate reason for this leakage is RFI suppression. I guess it could be interesting to measure both AC and DC current. I'd expect no DC current.