A simple cheap-o plug-in receptacle tester is what you need. I have seen them for two-dollars in hardware stores. Little yellow and red lights and an easy to decipher color-coded Rosetta-type graph. My five-year old understands how to read it.
Never EVER use a metal case appliance without having a functioning earth ground.
If you look at factory 2-prong cord appliances and accessories, they have 100% plastic cases.
In addition....
Power supplies have minimal but very important filtering components inside (MOVs) that either have a valid path through the power cord to earth ground or the protective circuitry becomes valueless. One of the ways I separate garbage electronics from the herd is to look for a 2-prong receptacle cord.
IN A PINCH...
I use a 3-prong to 2-prong plastic adapter block. With a concrete or tile floor, the little metal tab sticking out of the plastic adapter can have a jumper wire clipped to it with the opposite end dangling onto the floor. Place a micro fiber towel or big sponge atop the clip on the floor, then saturate with water. Keep moist.
This cannot work with carpeted, linoleum, or wood floors.
