Mesorah: It’s by the Zugos Gemaras in the tenth Perek of Pesachim. And it seems (to me, at least) pretty clear that there are some types of Ayin Harah that affect the world no matter what and some that only affect people who are concerned about them.
About the Chamsa, it is an almost universal Avodah Zarah symbol stemming from many religions. Interestingly enough, another early Kabbalistic symbol is also used in almost every mythology to represent some form of Avodah Zarah. That symbol would be the hexagram, or more commonly known nowadays as the “Jewish Star”/”Star of David”. Both symbols are said to hold Kabbalistic powers. While I am very skeptical of Jews dealing with anything that sounds like Avodah Zarah, it is not outside the realm of possibility that Hakadosh Baruch Hu imbued certain symbols with certain “powers” and that the Ovdei Avodah Zarah discovered this in the same way that Kabbalists did. I would still stay away from anything involving them though.