It does what it promises. Overall, it can power devices UP TO 900mA. The additional power supply (5 volts) is optional.
However, BEWARE. It does not include a power adapter in the package and moreover, its socket is quite specific (it requires a 3.5*1.35mm plug) which is a bit hard to find (you can get it from China for 1€) and usually does not end in a male 220volt socket but ends in a USB-A which requires an extra simple adapter to fit into a regular 220volt socket.
4 stars from me due to the lack of power supply.