Review on Cable Matters 3-Pack UL Listed 2 Prong to 3 Prong Adapter: Convert Your 2 Prong Outlet into a 3 Prong Socket with Ease by Keyone Brownlee

That weird little green metal tab on the bottom of the adapter really does serve a purpose. This allows you to ground the component you connected to the 2 to 3 pong converter. The correct way to do this is to attach (solder) a wire to a small metal tab with a hole in it, and attach the other end of that wire to a ground rod, electronic ground, or other nearby metal surface. The third connector you bypass with the 2 to 3 pin adapter is the ground pin, which is a safety feature. If you don't do everything I just wrote about, your installation will become insecure.