USB cable positive negative polarity and voltage output

Just for reference negative and positive polarity of USB cable - commonly positive is connected to the red cable while the negative is black. The other two connectors in the middle belongs to the data transfer cable if applicable. If you are still confuse and unsure place an LED bulb and connect it the USB to its power adapter to confirm - where the Bigger flag should connect to negative and smaller flag is positive - see picture below

The standard voltage output for USB drive is usually capped at 5~5.1 volts - and this step down power reduction is done in the USB power socket plug. Most computers, laptop, phone chargers plug USB slot are capped at the standard voltage. It can be altered but there is a reason why it is done that way.

Generally the USB negative positive terminal polarity is universal and it applies almost to all. So this is a small knowledge but it's important if you are dealing with USB connection fix.