It depends on what you mean "test". Many modern 24 pin power connectors from a power supply can no longer be split into 20 and 4 so you might have trouble physically plugging the tester into the cable itself. If you manage to get it plugged in it should work.
So how does this tester really work. Are you trying to insert it between the motherboard and the power supply or are you testing just the power supply itself on your desk. It takes nothing special to test a power supply. You just need a paper clip and a simple voltage meter.
Testing the power inline is much more of challenge and I would not try to use old test equipment with modern computers. They make all kinds of fancy testing equipment that will actually show you the power consumption on each pin rather than the simple voltage. The price has come way down but really is not something even your hobbyist computer guy would have. It is more a repair shop or maybe someone writing reviews that would need this specialized equipment.