Is it safe to power Arduino project using a power bank and wall charger? I got an Arduino project that need a constant source of power. Rather than dealing with batteries, I want to use a power bank like this:



Better yet, I want to keep the power bank plugged in to the wall outlet using a wall charger like this:



The USB wire coming out of the power bank, I can modify it and connect it to the 5V on the Arduino (Pro Mini 5V version). Is it safe to do so? The application uses a stepper motor that draws around 200mA and only runs intermittently. 

Thanks
Yes you can.  A promini will run very well on 5V from a wallwart.  Connect 5V to VCC (not RAW or VIN).  You can also find wallwarts with 2.1mm/5.5mm plugs, and a mating barrel jack adapter that ends in screw terminals so you don't have to try hacking up a USB cable.

Power bank, you will have to play games to convince it that something is connected and drawing sufficient current to keep it turned on.

Wallwart example  https://www.mpja.com/5-Volt-DC-Plug-Power-Supply-4A-Regulated/productinfo/18520+PS/

Barrel jack to screw terminal adapter example  https://www.mpja.com/55_21mm-Power-Jack-Screw-Terminals/productinfo/19454+PL/