Mod to ST70 - what's the use of extra capacitor?

Recently, I had the time to go through the assembly manual of my ST70 and also took a look of it's wiring under the chasis. I found that there is a capacitor (450V 100uF(m))(as shownn in the photo) connected between lug #1 of the filter cap and the chasis (ground). This capacitor does not appear in the wiring schematic of the manual. So, it appears that this is a modification by the previous owner. Anyone knows what is this capacitor for? Should it be disconnected? Thanks in advance for your help.
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Hi Bob. I've been trying to include a larger picture for better view but so far not successful. Anyway, I'll try to describe it in more detail. The +ve thread of the capacitor in question is connected by a short wire to the quad cap's lug facing the back of the amp (this lug is shown as #1 in the ST70's assembly manual) and the -ve thread of the capacitor is connected directly to one of the two solder lugs - the main grounding point of the amp - next to the quad cap. Hope this would help to determine whether this 450V capacitor should stay connected or need to be discarded. Thanks.

Thanks Bob. So, this "helper capacitor" is there to augment the two 50MFD output capacitors and hence improve performance. While disconnecting this capacitor will not diminish performance, will there be better results and larger margin for safety if this "helper" is replaced by one with higher voltage and larger uF? If yes, what would you recommend?
BTW, on closer cross examination with the wiring schematic of ST70's assembly manual, I found that there are a few wrong connections, namely lugs #1 & #8 of V6 are not connected and the wire from point 16 of the PC driver board is connected to lug #2 and NOT lug #1 of the right power take off socket. I really look forward to hearing any difference when these are corrected. Since the majority of ST70 are not factory-wired, I guess it is necessary for a new owner to take a closer look at the wiring of his newly-acquired ST70.

I clicked into JJ Electronics www.jj-electronics.com and found the 500V 32 + 32 uF capacitor (model TC529) but couldn't find the price. Do you know how much? By the way, can I upgrade the existing two 50uF output capacitors to ones with higher voltage and do away with the "helper capacitor"? Thanks for your time Bob.

Parts Connexion has that cap for $9.95

the JJ 50+50 cap is $8.50 at www.tubesandmore.com and shipping is probably less money also
part number is C-EC32-32-500

Thanks guys for the supply info of the cap. But I'd still like to know if in fact similar improvement can be obtained by upgrading the two 50uF output capacitors and then disconnecting the "helper capacitor". Thanks.