[Arran]

 Yes, that can was added as a old repair, the original wet electrolytic probably dried up and in effect went open circuit. There were a lot of service shops, and even more amateurs that used to do that, even though every technician's course, and even some factory service manuals, told them not to.
  This very afternoon I was removing a very similarly mounted can, though I am not sure why it was added as the originals were, and still are, functional. They connected a two section twist lock can under the chassis with each of it's 10 uf 450 v caps in parallel with the two main filter caps in the original can, wired in directly below. My guess is that they wanted a hum free set so they decided to add the extra caps under the chassis. However even though two of the sections of the original twist lock can were good, the third 10 uf 450 v cap was starting to fail, but it was connected to the plate of the RF amplifier tube. I'm replacing them all, they may work now but the newer can was put in there in 1962, the original in 1940, so time for something made within the past decade.
Regards
Arran