What do you hear with a better/bigger power supply and output capacitors in same amp?

Music, not necessarily better

I'm speaking in regard to my experience with older chrome bumper Naim Audio gear.  IME, the difference between using a Naim NAC 42.5 preamp and NAP 110 power amp on their own vs with a dedicated HICAP power supply: Lower noise floor,  greater sense of control, better PRAT. At first differences are subtle but appear to be more noticeable over time.  I never regretted spending the extra money for the HICAP.

Thank you everyone for the wealth of info on this topic. I am learning a lot more than I had known prior to asking. This is not a DIY question although the responses should help those folks.  The nuts and bolts of this are:

A:  one Kismet Stereo:  claims 160wx2,  (850VA toroidal, 4qty x 35mf caps total, 70mf/side)

B:  two Kismet monoblocks, per amp:  200wx1   one 850VA transformer and 140mf output capacitance (each channel has twice, plus the entire audio board too).

Now we're down to brass tacks. Might I expect to hear subtle gains in noise floor, PRAT, piano weight (e.g.) bloom, etc?    I experienced a lot with the Kismet stereo. Is it wishful thinking; have diminishing returns set in?  Thanks all.

I purchased 2 Acoustat TNT200’s to have rebuilt and converted to Monoblocks.

They were purchased to power my Acoustat Spectra 33’s, which I also have rebuilt and upgraded. Before the conversion I used 1 amp in stereo mode to power the Spectra 33’s and a Acoustat passive sub that came with the panels. Sub sounded bloated soft and slow. The panels alone sounded good but did not deliver what I was expecting from all the hype surrounding these panels. I was ready to sell the lot. Fast forward, panels are rebuilt, amps are rebuilt, pushing somewhere around 900watt @4ohms per side. These things sound spectacular, airy, controlled and Soundstage that puts you right there. Base on your comment, no not a bigger transformer or larger caps, rebuilt transformers and new caps. Each amp is now a monoblock which essentially more than doubles the power rating. This makes a big difference at low listening levels. Dynamics from a Electrostats is rare. IMO, improving the power supply and larger caps associated with what’s required for those upgrades, would give you a better sounding amp. Converting them to monoblocks would be enjoyment ×2....

OP, keep in mind that bridging stereo amps into mono isn't a free lunch.  For example many stereo amps don't do well bridged into 4 ohm loads.  You need amps rated stable down to 2 ohms do that.

Monoblocks typically are not bridged stereo amps, though, so true monoblocks stable to 4 ohms would be fine.