The current from a power supply is a max rating. If your system draws less, then there is less current created from the power supply. No need to do anything, just plug it in and use it.
I have heard different estimates for 12V supplies and it varies based on which ATX supply you have, but if your numbers are accurate, it should be fine. (of course, if it all blows up and burns down your house you can't blame me. I make no guarantees on my advice and it's worth what you paid :-)).
One more thing. Make sure that 19A rating was for the 12V supply. They will have different ratings for the 5V and 12V supply and usually the 5V source is larger.
I have heard different estimates for 12V supplies and it varies based on which ATX supply you have, but if your numbers are accurate, it should be fine. (of course, if it all blows up and burns down your house you can't blame me. I make no guarantees on my advice and it's worth what you paid :-)).
One more thing. Make sure that 19A rating was for the 12V supply. They will have different ratings for the 5V and 12V supply and usually the 5V source is larger.