4700uF is enough for 4amps ...
47000uF if i read that correctly is overkill
I think you are missing a number of considerations. For a start, most 4700uF caps cannot handle 4A continuous, but even if it can, that is for a new capacitor and they degrade with age.
If you use a 4A rated capacitor in a 4A supply, you are designing a bit of gear that you only expect to last a year or two. Put a bigger capacitor in and it can easily last 30 years without a problem.
Next issue. 4A from a 4700uF cap means over 8v p-p ripple. A 47000uF capacitor has less then 1V p-p ripple, so you can get an extra 7 volts reliably from the supply.
If you take a 30V 4A supply that uses a 47000uF capacitor, and replace the capacitor with a 4700uF one, you now have a 23 volt power supply.
Another consideration is the supply output ripple. Say your supply regulator has a 80dB ripple rejection from the input. An 8V p-p input ripple would give a 0.8mV output ripple. A 0.8V p-p input ripple gives a 0.08mV output ripple.
Given all that, selecting a large capacitor may easily be worth the extra price.
Richard.