I realise that this is an old topic, but the following may be of use to other intrepid charger repairers.
The Mitsubishi iMiEV has a Nichicon On Board Charger that appears to be similar in many respects to the one in at least early Leafs. For example, compare the OP's burned capacitor (it might actually be a relay, or two small capacitors near the relay) with the AC filter from an iMiEV charger:
I note that the components that frequently blow in the iMiEV chargers are the small blue (with green tinge) capacitors to the right of the potted "cage", and the square component near them is a relay (the pre-charge relay), not a capacitor. The Nissan charger has three pre-charge resistors (white blocks to the left of the cage), whereas the iMiEV charger has only two. One of the iMiEV pre-charge resistors is larger than the other, and contains an integral fuse. When the iMiEV small capacitors blow, they can cause quite a mess including that black muck, and could well be the cause of the OP's fault. I'm not convinced that the OP's large capacitor (which I think may be the PFC capacitor) has vented; it could all be "fall out" from whatever happened in the AC filter cage.
The cause of the iMiEV charger failures is not yet determined. One of the prevailing theories is that when the charge is suddenly interrupted for whatever reason (mains failure, in the iMiEV's case it could be the 20 A DC fuse on the charger's output going open circuit from metal fatigue), the energy in the charger's inductors has nowhere to go except into those tiny capacitors, which can't absorb that much energy, and consequently fail spectacularly.
Edit: there is a lot of useful information in the following myimiev.com topic, including some partial schematic traces (only at the edges so far, but includes the AC filter components
), and even an intriguing X-ray photo of the Waffle Plate™
(a potted assembly with most of the high power semiconductors).
Troubleshooting and repair for On-board Charger (OBC), DC-DC Converter
2012 Leaf with new battery May 2019. New to me June 2019.