Thanks. I just tried again. My charger has two USB outlets, which apparently different: it didn't work on the N/A (Non-Apple) outlet but is charging happily on the A (Apple) outlet. Issue resolved.
The old chargers have labels for Apple, Samsung, etc. Newer chargers no longer have these labels, and incorporate smart device detection, which sets the charger so that it is compatible with the device. Aukey, for instance, calls their's Aipower.
The way Apple (or other companies) detects whether a charger is compatible, is by looking for a small voltage on one of the Data leads. If it is missing, or too far off, then the device will not charge. I found this out when trying to figure out why an old speaker dock would not charge an iphone. It's surpising that they are able to do this using the USB standard, which only has 4 leads, Grd D+ D- 5V