To charge your Power+ from the grid you can use a micro-USB cable and charger. This is the same cable and charger as used for an Android charger for example, and it is sold at most electronics stores. You can also use an iPhone-charger (only with 5V output model) together with a micro-USB cable (not a lightning cable).
Whilst charging via the grid one of the green lights will blink. This light indicates which ‘quarter’ of the battery is currently being charged.