Electronic – Un-insulated Ground wire in USB cable

Both options 1 and 3 are perfectly acceptable for power-only. If you want less noise on the power supply you should probably go with option 1 - tying the shield pins to the ground pin of the USB port. For signalling as well, 1 is the better option.

For power only, bear in mind you should not try to draw more than 100mA without negotiating with the USB host for more. Be sure to factor that in when deciding if the load can be driven by a USB port.

USB cables do require some precision engineering. There are stringent requirements on value of differential impedance, quality of interconnects, and amount of losses per cable. The high-speed part of USB cable, even at USB 2.0 480 Mbps data rate, is made of a twisted pair of wires, all wrapped into a shield. This makes it a "bi-axial" cable. The cable is done as uniform as possible, by exercising good manufacturing discipline, which reduces wave reflection/scattering as signal transitions/edges propagate along the channel.

However, all "complex calculations" were done fifty-seventy years ago, and the net result is rather simple.

The characteristic impedance of a twisted wire (or planar waveguide, or coaxial cable) is a function of conductor geometry and dielectric constant of the insulator between the conductors. To make it 90 ohms differential two wires of certain core diameter and certain thickness of insulator are twisted together (at certain number of twists per meter). The twisting ensures that the distance between wires stays constant, because it is a major parameter that defines uniformity of the transmission line. Insulation thickness should be also well controlled, for the same reason. The number of twists per unit lenght is also important, but to a lesser degree.

Now, the insulation diameter defines the distance between two signal conductors, and electrical properties of this geometry were calculated long time ago. So a manufacturer of USB cable (I mean bulk cable) knows what diameter to pick, which kind of insulation to use, and how to twist. The final selection of wire parameters goes through experimentation, where the cable quality and parametrics is measured by special equipment. After which the raw cable goes into production, and sold to cable makers, who solder chunks of it to a pair of USB connectors, and encapsulate the ends by pressure molding.

So, USB signal wires do have a special treatment.