I'm always astonished by how often this same question comes-up and even more by some of the answers given.
Although I have overlooked the problems of safe probing on line referenced equipment myself in the past, it is a really important point to understand.
Anyone wanting to work on live equipment should go to the trouble of first understanding how electricity is delivered to wherever they are using it, the role of each wire used up to the socket, the existing protection equipment and it's condition if something does go wrong.
Beyond the financial aspect of a failure the question you want to ask when working in your lab or garage is: "If I touch this how much current will I be taking?" When "this" is your oscilloscope Ext. Trig. BNC or handle the question should become worrying.
If you aren't worried at that point you may as well take the reasoning one step further and double wrist-strap yourself with a nice low impedance to the local ground, it has potential to roast your fingers off, but may at least save your chest.
There are well known good solutions for probing on 220V, they do have a low cost compared to an oscilloscope or funeral.
Is it really worth putting your relatives to all that bother for a bloody 9$99 power supply that should have been better designed in the first place?