The amperage you'll need depends on the load, in this case, your strobes. If you already have a power supply that's rated for 1.5A it's probably sufficient. Try it out and see if it powers all 3, it won't do any harm if it's not enough but I'm guessing it will do the job. Just remember that voltage is the important part of any power supply, it must match the requirements of the device. The amperage rating of any power supply is merely the maximum that it's capable of, if the rating is more than what is required there's no harm, the load will only draw what it needs. If the amperage is not enough, it won't power the load.