Why do you feel the present alternator wont cope with the load?
Whats the total wattage of the fogs?
A general check is to start the motor and let it idle with no lights on.
Then turn on the fogs, note the brightness.
Then rev the motor to around 3000rpm and check if theres any major improvement in the brightness of the fogs.
If there is, your may need to uprgrade.
You can install HID bulbs to your fog lights or spots. they require half of the power halogens need and if you choose white color their light output is more than twice. So stock alternator can cope with them.