Hello,
I have a 9V powerbank, and could adapt or find an usb to dc connector (round one) to have this powerbank input passing through a +/- connector that i could connect to some DIY box.

I would like this DIY box do this :

-If electricity coming from input 1 current (normal plug to 220/110VAC), power device with it.
-if no electricity coming from input 1 current, instantly (could be the problem, no power cut more than 1sec should be done, if possible none..), take current from second input, my 9V powerbank.

I don't know in circuit. At least what a capacitor does, that a diode protect from reverse polarity, a fuse burn and protect from overheating..

 

somebody can help?

 

It depends on what

electricity coming from input 1 current

means. If it's a higher voltage, you can do this with just a diode.
You left out so much information nobody wants to guess the voltages, the currents, the DIY box, or drag it out of you one question at a time. Give the information or nobody will guess at what you want.

 

INPUT 1 : DC 9V (Battery)
INPUT 2 : DC 9V (power adapter)

If input 2 no current, directly switch on battery.

I want something with input 1 and input 2 to output 9V-DC.

 

still looking for a solution. hope you can help guys.