1. Yes, 12V is ok, in fact, the power adapter we ship with OS Latch is 7.5VDC. The controller has built-in voltage booster to generate the voltage required to open or close latching valves, so it’s insensitive to the input voltage level.
2. OpenSprinkler Latch uses standard DC power adapter plug where the center is positive and side is negative. If you search “male dc adapter” on amazon, you can find plenty of adpaters or cables that can convert between wire screw terminals to DC plug, such as this:
https://www.amazon.com/Xenocam-2-1mm-5-5mm-Camera-Adapter/dp/B01AGQVYQQ
Before using them, make sure you double check the polarity: center positive, side negative.