"i am looking for some tutorials on power supplies which can be used in commercial projects. i am not a master in analog electronics to i have to rely on helping material for this."

If you are designing a power supply for a commercial project, the amps & volts are probably the least of your problems!
Remember, the power supply connects to the live AC mains - so there are major safety issues here.

You would therefore be much better to just buy-in a ready-approved, tested PSU.

If you look at most small mains-powered appliances, you will see that they've done exactly that: the product just has a "DC in" jack, and they buy-in an appropriate "wall wart" power supply.

An external PSU also means that your product is releived of all the mains-related safety approval issues.
It also means that you don't have to worry about different connectors, voltages, etc, etc in different countries - you just ship your product with a US adaptor to the US, a UK adaptor to the UK, etc, etc