WHY DO MY 40W LASER POWER SUPPLIES KEEP FAILING?

check your in-going power and make sure that you have a good neutral connection. Frequently the issue is not the power supply but the power coming into the power supply that causes the problem. There is a chance that the power is good coming in but there is a loose neutral connection and that causes it. This is the neutral connection that runs all the way back to the panel in your home.