How do I find the specs for transistors in order to replace them?

Find the Transisitor’s P/N and go to a list like THIS

The markings maybe laser marked or found on the circuit board.

@Tropical_Willie is right the part numbers are often laser-etched – and that’s a low contrast marking unfortunately.

If the parts are so fried you can’t find any mark you might be able to determine what would be appropriate by analysing the rest of the circuit. In a power supply board a relatively wide range of part might work. You’ll have to figure out polarities to get the right kind of part, and figure out the maximum voltage that the part might experience. Get replacements that are rated for at least twice that voltage.

A data list is here: http://category.alldatasheet.com/index.jsp?components=TRANSISTOR