What I would typically do if something is not working is measure the voltage at the primary for 120 VAC with a multimeter.
Then measure the voltage at the secondary.
Then go from there.
Very rarely have I ever needed to replace a transformer for a non-working electronic power supply. Usually no main power, fuse blown on the electronic circuit board, capacitor, or voltage regulation components (main power regulating transistor).
What is the problem you are having?