This is not a power converter, all this does is changes the plug (its sad I have to say this but I have seen people Actually confused by this point) IF you plug a device into a 220V 110V only socket you want to let out the magic smoke and your device will no longer work. This only Allows you to adapt a US standard 2Prong plug to a Schuko standard 2prong or 3Prong plug.
This style of plug has been critical to being able to use wall word in Schuko receptacles (the big square "Transformer" that plugs straight into the receptacle and has a cord going to your device).
Many other 2 prong adapter have a rim on them did stop you from using odd shaped plugs or wall word. I highly recommend thesis !!
I bought mine as a 10pack for 9Buck a few more than I need today, but a few extra-is always nice.