I just found one photo of the LP-E6 charger with ratings listed, and those show output 1000mA at 8.4V while 5V 2A input is provided as input.
Since the OP post is for the LP-E17 charger, I found this which shows the actual product label and it says input 5V (no input current) output 4.2V / 8.4V 500ma. Puzzling, dual voltage for a single battery type?!
Continuing the search for info on the 5V USB charger, I found another actual product label for a different manufacturer's product which says input 5VDC 2A 10W, and output 8.4V 0.6A 5W
More believeable. But it would take THREE HOURS to charge a single 1800mAh battery
It would take longer than three hours. You can ignore the Voltage output spec. Li-ion chargers are CC/CV. Constant Current, Constant Voltage.
They charge at a Constant Current until the battery reaches 4.2V then slowly reduce current, keeping the battery at Constant Voltage of 4.2V until it is fully charged.
So for a flat LP-E6 the output voltage would start closer to 6V but that is just a result of the Current which is what the charger is regulating.