Power Supply Lightning Protection
You're really asking the wrong question. If you're thinking about selling something that plugs into the wall in any volume, step back and figure out what the applicable UL standards are. There will certainly be some kind of surge test along the lines of IEC61000:4-5. There will be creepage, clearance, and isolation requirements. There will probably be a maximum acceptable temperature rise as well. If after figuring this out you still want to create a product, you would be smart to hire a consultant to review the design before going to UL for testing. This may cost a few grand, but failure will be even more expensive.