The point being, if the power supply is not capable of
supplying the current required on SSB voice peaks, then the
power supply is too small to start with. The logical 'cure'
for a 'too small' power supply is a larger power supply. Any
thing else is a 'kloodge', a crutch to prop up a cripple.
A capacitor does supply some additional current to the
system if it's large enough, but even with very large capacitors
the supplied current is going to be very, very tiny in relation
to the total current draw. Something else you should remember
is that the power supply is also going to have to charge or
re-charge that capacitor when it is drained. That means that
there is no increase in total current in the system, in fact,
there is a decrease since capacitors are not 100% efficient
(they do have loss). This means that the current demand on the
power supply has increased and the 'hole' is just getting
deeper.
Capacitors 'work' in audio systems because they 'rob' current
from one part of the audio signal and 'deposit' it in another
part of the audio signal. If the purpose is to accentuate the
high frequencies, then the 'extra' power is robbed from the
lower frequencies (or visa-versa). The total average power of
the audio signal is not changed (increased), it's only re-
ditributed.
Some things with audio system do carry over in to RF power
amplification systems, but the use of capacitors in the way you
want to use them, isn't one of them...
'Doc