1. Yes, sinking. But depends on the scheme of execution and applied wire.
2. Not necessarily a private matter of the producer's standards, this requirement is not described.
3. Nothing will happen, it just will not give more than its nominal value. But burn or no, it depends on the scheme performance and the level of "kitaychiny".
4. You can't take from the source of current is more than he can give. Fuses are to protect from short circuit, from the rest it is not necessary.
5. Please do not use them for purposes not intended for them. 5V/1-2A their nominale. And again, all will depend on what is the quality of the connector - poor contact, for example, that subsidence and heat = failure.
6. Depends on the manufacturer, standards are not described. But most of the support for this does not interfere.
1. The charger (or any charger with USB host) is sinking when it is taking more current than it can give. In normal mode, the output voltage of the charge is maintained at 5.0 - 5.2 V
But on the other end of the cable is already possible drawdown! The higher the quality of the cables and connectors they use, the less voltage SAG. (because it will not work to squeeze 2A using a bad cable - the voltage will drop, the phone will see it and curbs the appetite)
2+3. USB (up to 2.1 including) requires manufacturers of devices to consume no more than 0.5 A when running. In USB 3.0, the threshold is raised to 1A. Moreover, the USB host is not required to support devices with even consumption 0.5 A - for standard, on initial connection, the device tells you how much amperage it requires to operate, and the host replies, can he provide. According to the standard, upon initialization the device must not consume more than 0.1 A
And here comes in the industry of phones and a standard connector for charging microUSB. When the standard USB is designed for communication, have begun to use "stupid" to provide devices with power, began the confusion. If you connect to PC the phone could "ask" how much current it can give out, "dumb" charging not supported no initialization and connection establishment, and they could take ... and how to learn, how much you can borrow amps from a charger? What is the current consume the phone when stuck 5 volts?? And actually, suddenly it's not a dumb charger, and cable with broken data bus connected to the PC, which can not take more than 0.5 A???
In General, it is invented to check whether the shorted data bus, and if shorted - to take, for example, 1A. Other manufacturers of the same Apple charging was applied on the data bus a specific voltage that the phone was identified, recognized the charge as "a" and consumed, for example, 2A.
Then Qualcomm came up with QuickCharge, made a smart charging let cable instead of 5 volts as much as 9. In the new versions, the voltage increased to 12 at all and then to 20. And all this via USB... something not brought me there. What's the next item?
4. The fuse device I not seen. Usually sags the voltage in volts commercials to four. Such naprugi phone can not take a lot of amps and automatically reduces current consumption.
5. Standard voltage, which theoretically can charge devices in the range 4.0-5.5 volts (I have a charger with 5.5). With QuickCharge 3.0 - voltage up to 20 volts. Depending on the quality of the cable, through it can flow to 2 amps. Well, a maximum of 3, no longer will overheat the contact and all poplavyatsya nafig.
6. In what direction? Charging is generally a side thing in the USB standard. If you're talking about connecting the phone to PC, in which he is charged - usually always works. If OTG on my phone I was able to make sure that he also has been charged. But not always. In this mode according to the USB standard, the phone should serve as a source of power, and not Vice versa, to draw power from attached devices.