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.

i know volts, but i don't know Ampere's. one of my device which i want to operate requires 12V and i think 1.5 Amp. i want some handy concepts which i can use to meet my power supply requirments.

Also if i have 12V but a different Ampere's then the device requires then what will be the affect on device.


Also i want some circuit which generate +5V, -5V, +12V and -12V. is there any web site from where can i download them.


Thanks
Shahzad