My company uses that gear. I've had some that work fine, but a fair percent can barely maintain a charge. I've actually had some lose power while "charging."
I believe some electronic flight kit tablets are currently FAA authorized to charge (but not operate) off 400 Hz cockpit outlets.
Airbubba, an often overlooked nuance, that in reality, is not enforceable. Use inflight, charging inflight, and charging while use inflight are all issues to be looked at. The temptation to charge other devices is also uncontrollable.
As noted by several posters, there are issues with the 115v chargers. Potential for EMI is there, as these chargers do not offer 2 way protection. While the aircraft 115v system has protections built in, it depends where, and what happens back to the protection.
The typical chargers were never meant to run on 400HZ. Switching supplies have PFC controllers and they don't work properly at 400 Hz. The controllers can cause considerable amounts of leakage current back into the equipment grounding conductor. this is where the 115v 400 Hz plug falls short.
The power plug referenced at the beginning is a DC plug and offers full protection including EMI. It is important to note that this is safe for all of these devices Apple, and non-Apple.
The iPad is not the only tablet of device in use on the flightdeck. Are phones permitted to be charged on the flightdeck? With that plug, other devices can be charged safely and without EMI. I dont have any vested interest in that plug, other than its use.
I really dont think the quality control on the out of the box charges is sufficient, even from a company like Apple.