USB Power Supply Cable 9V (500mA max.) with DC Barrel Plug 2.1/5.5mm.
Do the math: To achieve 8.4W (0.7A @ 12V) output power, you will need a USB port that can deliver at least 1.9A @ 5V at an expected efficiency of 85-90%.
Total length about 90cm (3ft).
Power supply cable for devices and CANADUINO® DIY soldering kits with 2.1/5.5mm DC barrel connector voltage input.