I used to live in a home for fifty (50) years which was originally built in the mid-1950s. "None" of the electrical outlets were grounded outlets when we took up residence where the outlets would accommodate a 3-pronged plug. Before I swapped those 2-pronged plugs with 3-pronged "grounded" wall plugs (Warning!--Don't risk doing this unless you really have the knowledge of how to perform the task safely!), I would (when needed) go to the local home centers and purchase "adapters" that would plug into the 2-prong outlet and convert it to a 3-prong outlet. Those adapters even had a brass colored clip that you would position under the screw that secured the electrical outlet's trim plate. I "thought" up until I read what follows below that that meant the outlet was properly grounded. To answer your question, I entered the search term "Is it safe to use a three prong adapter in a two prong outlet?" Several entries indicate that a three-prong/two-prong adapter is also known as a "cheater" plug by those possessing knowledge of electrical matters. Further indication is made that if you are in an older house that does not have many, or any, three-pronged outlets you might be "tempted" to use a grounding adapter or three prong adapter to circumvent this obstacle and still use your devices. It will work, but whether it is safe for you or your electronics is something else to consider. Indication is made by some that there are advantages to employing "cheater" plugs in that they allow you to use electrical devices in areas where you normally would not be able to use them. You can purchase a three-prong adapter at just about any store you visit and don’t require anything to be re-wired for use. However, there are also "DISADVANTAGES" to using cheater plugs! It is mentioned that cheater plugs are not designed to be a safe solution to powering a three-pronged electrical device. Electronics have the third prong to protect from electrical malfunctions, fires, and electrical surges. When you remove that functionality it becomes easier for the electrical device to break, and cause further damage. The grounding adapter does not function in the same manner as a grounded circuit. If an electrical issue such as an electrical surge occurs in the electrical device the electricity can cause electrocution and electrical fires. Many people are not aware of the drawbacks and assume that because the products are sold in stores that they are safe to use in the home. Further information is provided about the questionable safety of completely removing 2-prong electrical and swapping them with new 3-prong electrical outlets. Indication is made that they, too, must be "properly" grounded. For further review, please review the entries on GOOGLE or YouTube and/or consult with an electrician or someone who has proven electrical knowledge.