Unfortunately, Apple has built in some propritaryness in their adapters and even though the LG adapter is rated at 0.7A, it may only be able to charge at 1 amp. It's basically a guess, since there is no way of telling. How Apple requests say more than 1 Amp is propreitary. USB charging ports may support it, but even the data and the chip are not readily available.
Motorola has done the same with their phones through the use of resistors on the data lines. To get the higher charing currents, you need the Motorola charging cable. It's not necessarily based on the current available by the charging port, but the actual cable to tell the phone that it wants a higher current to charge.
Some of the wierdness is described here:
https://en.wikipedia.org/wiki/Universal_Serial_Bus
In another example disk drives may need a special "Y" USB cable with TWO USB connectors that go to the laptop and 1 that goes to the drive. It then takes 0.5 A from each port on the host side.
Hubs on the other hand may not be able to supply the required power at any price. Many might limit the port draw to 0.1 Amp.
Now, I have used a USB isolator to be able to supply the larger current from a 0.1 A Hub with success and also unsuccessfully.
In my unsuccessful attempt, I was charging a Motorola Backflip and had it tethered to the Laptop. Power drain is such that the battery will die faster than the phone can be charged.
In a successful attempt, the Isolator was able to power a USB modem.
5.1 Volts is fine for a 5 V system, but I would not go higher. That is actually +20%.
A datasheet for a 7404 which is a typical TTL part says the recommended operating voltage is 4.5 to 5.5 Volts with an absolute maximum voltage of 7V. Much of current technology has inputs that are TTL compatible which means that they respond to the logic levels of the TTL system of high and low. Protection for TTL compatible devices as inputs might consist of only a resistor that limits the current.