EE/CE here: In order if your questions... 1. Assuming you hooked the 5V to the USB 5V and the GND to the USB GND pins, nothing bad would happen. 2. Nothing wo

EE/CE here: In order if your questions... 1. Assuming you hooked the 5V to the USB 5V and the GND to the USB GND pins, nothing bad would happen. 2. Nothing would get fried 3. Plugged in devices would respond according to how they're designed. Most cell phones will limit current and only draw 500mA if they don't have any other signalling to test otherwise. Some will slowly ramp current until their own internal limits if voltage drop isn't too bad. Some 'dumb' devices will pull as much current as they 'want' or need. You won't be able to push 30A into any device because there are almost no USB devices that 'want' that much current. Even really poor behaving devices (outside of outright broken ones) will probably only draw 3-5A max. Technically this is non-compliant, since there are defined USB specifications for how USB ports should be connected. If you wanted to make a 5V 'mega USB' charger, here's all you'd need to do: Take your 5V, many amp power supply and connect all USB-A ports you want to it, with a constraint that number of USB ports should be total amperage divided by 2.5. E.g. if you had a 10A supply, only use 4 USB ports. Short the D+ and D- pins together on the connector. 5V should be connected to your large 5V rail, GND should be connected to ground. That's it. You've just made a 'DCP' (Dedicated charging port) device. By USB standards any device connected can pull up to 1.5A; in practice they'll usually pull 2.1A or more if they can.