I have a Samsung Note 5, an OtterBox Defender, and the Samsung OEM Fast Charger (circular in shape, if that has any bearing.)
The wireless charger would NOT work with the Defender case, and I brought this to both Verizon Wireless (from whom I purchased both the case and the wireless charger) and to OtterBox's attention. I was forced to charge the standard/direct connection way, which upset me because of the price I paid for the wireless charger- and, the Verizon Wireless rep assured me that the charger would work with the OtterBox Defender case.
When connected, the blue light on the wireless charger would begin to flash after about 30 seconds, indicating that it was not charging the phone.
Some have suggested that I should remove the OtterBox's rubber protective casing. There are two problems with that. One is that- it still won't charge even if I remove the rubber case. The second is- even if it would charge, it is very difficult to use the phone's buttons without the rubber case on.
At the suggestion of someone on a related forum, I, too, purchased USB micro USB charging cables from Anker (via Amazon)- the PowerLine+ model. I am pleased to report that the wireless charger is working properly now with the OtterBox Defender and rubber casing.