Hardwiring Keypad w/existing two-wire setup

I want to utilize the existing black/red power wire from my old alarm system. I plan to purchase from Amazon, [j4home DC-DC Converter Step Down Module 12V to 5V Micro USB Power Adapter](https://www.amazon.com/gp/product/B07RDGR9GF/ref=crt_ewc_title_srh_1?ie=UTF8&psc=1&smid=A2Q4NRU851RDPH) I would also like to use my existing power adaptor if it's appropriate. [url=https://postimg.cc/yJDP6rHq][/url] Will this adaptor be adequate? If not what power adaptor should I purchase, on Amazon preferably? Thank you in advance, Dan