Could anyone point me in the right direction with power to the RAMPS 1.4

I have a new 12V 10A laptop style power supply from Maplins with a barrel connector. I was planning to buy the opposite connector component for the barrel and then wire it into the green terminal block on the front left hand side of the RAMPS.

There are 2 + and - though???

Also, does this power the Arduino MEGA or do I need the PC USB plugged in?
I will probably have the USB plugged in to start with until I buy the card readed and LCD.

By the way, I am going to power 3 steppers for the Delta vertical motion, 1 stepper (maybe 2 in the future) for the extruder and no heated bed. (Using PLA)

Thanks for any help you may suggest.

Steve

The outside connector is to power motors, hotend,and D9, if used. Along with power to the boards. That is the one you must connect. The inside connector is for the heatbed. And with using a 10 amp PS, i guessing you are not using one. If you are that power supply won't work, it is too small. You would need at least an 18 amp and that is maybe too small.