Amp not enough power

you are so close to meeting spec and you'll never whatsoever discern the difference of 20 or so extra watts, even if you do achieve that.
Now if you want to tweak it for enhanced sound quality that that is a different motivation, and I wouldn't stop at just the power supply caps alone.

120V isn't input voltage...

First of all, are you certain the power rating has decreased over time? Have you had the same measurement when you first had the amp? Like someone else mentioned, it's within 5% of the rating. Maybe your amp was assembled that way.

Power rating is not like the maximum speed of the car where you measure the speed with full throttle. Power rating is measured *as relative to the distortion*. As the power goes up the distortion goes up after certain point. Are you sure you are using the same distortion percentage for clipping as published spec?

If I have to replace these 4 power supply caps, Can somebody know an electronic supplier who carries 19,000uf, 80v screw type Electrolytic caps. These are hard to search even in the net. Your help will be appreciated. I located some electronic parts supplier but a minimum is required to order ie 100.

Use 19000uf,100v screw type Electrolytic caps.
Cap made by Sprauge 19000uf,100v.Price 24 dollars each.
Length 5 inches long.
Cap made by sprauge 19000uf,100v.price 15 dollars.
Length 3 inches long.
It is Availiable at teddss.com
Always use higher than 80v.