PDP 8a transformer capacitor replacement?

[Brian Walenz]

Having read all sorts of bad things about these older oil filled
capacitors, I decided to replace the one on my 8a.  I got what I think is a
replacement - 6 microF, 660VAC, 50/60Hz, "NO PCB's" - but it is physically
about 1/3 the size as the original.

Did the tech for these get that much better?

What purpose does this serve?  It's hanging off the transformer.  I see
lots of links about motor start capacitors, but nothing relating to
transformers.

http://www.mouser.com/ProductDetail/Cornell-Dubilier/SFA66S6K288B-F

Thanks,
b