AFAIK they are conventional Bipolar power switching transistors, as shown on my Chinese tester, and from the circuit around them, but it may be worthwhile carrying out the test you suggest. This PSU has taken up a lot of time with, at the moment no result in sight, despite all the helpful suggestions from fellow forum members, for which, btw, many thanks, despite my tracing out much of the circuit, and replacing a known faulty, and several suspect components. This is galling to say the least! The circuit is similar to one on this website;
www.pavouk.org It is on the second page near the bottom (200W ATX Power Supply)