Can I use a 12volt 18 amp power supply on a system that asks for a 12 volt 13.3 amp
Many thanks to all that can help

 

Absolutely. The power supply you have (12V 18A) simply indicates that it can withstand higher current loads; or up to 18A. If you go over this current, the voltage will begin to drop significantly. Since you only require 13.3A, that is well below the maximum current rating.

Austin

 

so is the rule of thumb over amps ok but not volts

 

so is the rule of thumb over amps ok but not volts

Yes.

If the load is provided the proper voltage, it will only draw the amount of current that it needs.

 

so is the rule of thumb over amps ok but not volts

Well, that is true if the power supply is a regulated one. If not you will soon find out that the only truth will be the smoke out of your system.
If the power supply is regulated then its output voltage is held constant regardless of the output current (up to the rated value of course). However, if the power supply is unregulated the output voltage will equal the rated voltage only if the current drawn is equal to the rated current. Always use regulated power supplies for electronic equipment.