What is this symbol between the Volt rating and Amp rating?

That symbol means DC direct current. The power supply puts out 5vdc.

The power supply is a transformer that steps down the wall current (in some countries it's called the 'mains current') to 5 volts AC. Then it must be rectified to provide DC. In some devices the rectifier is in the power supply (like this one) but in some the power supply delivers AC and the rectifier is in the device itself.

The dotted line represents ground. The solid line is your current, and as you can see it's always on one side of ground, so DC.

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The dotted line is the x-axis, and the solid line is flat indicating Direct Current (DC). In order to understand electronics, it is helpful to make a water analogy. If you drill a hole on the side of a bucket, voltage is like the distance that the water squirts (high pressure squirts further). High voltages leap, like rubbing your feet on a carpet and watching sparks leap to grounded objects. Current, on the other hand is about the volume of water flowing as a result of the size of the hole. Large holes correspond to large currents. A Joule is a unit of energy. A Coulomb is a large quantity of electrons. Voltage is Joules per Coulomb. Current (symbolized by the letter I, measured in Amps) is Coulombs per second. Power is voltage times current.