Internal Power Supply Technology Changes since 1999?

I use an older very high end preamp with a separate power supply that is the same size as the preamp itself. .
The same manufacturer now makes better preamps,without the external power supply, that are about the same size as my preamp. What have been the technology changes that have simplified and presumably improved the power supplies?

ptss,
it is very likely that your very old hi-end preamp was made well before 2008. Pre-2008 people spent more $ on hi-end whenever they had discretionary income. All that changed post-2008. The point being your preamp manuf could make a cost-no-object preamp in a 2-box chassis & have a good chance of selling a few. These days that happens much (or much, much) less. So, one thought that I have is that your preamp manuf wised up & is creating the same preamp in a 1-chassis box so that it is less costly & more appealing (cost-wise) to consumers. There might be a compromise in the sonics but what's better - sell a 1-box preamp with some sonic degradation (if any) OR not sell a very costly 2-box preamp?

Are you sure that the newer 1-box preamps also use a linear power supply like your 2-box preamp?

With the advancement of technology esp. capacitor technology, cap sizes have gotten smaller for the same capacitance. That means a large power cap can be put in the same spot to do more filtering & create a smaller ripple DC power rail.
HEXFRED diodes (used in the bridge) have also become better in terms of higher voltage handling capability, faster recovery & spewing less RF content. This means the diode bridge is now much less of an RF generator.
Additionally, many good power supply designs use a small snubber capacitor to contain the sharp rise in voltage when the current flow stops  flowing in the AC waveform as it comes off its pos & neg voltage peaks. This too contains the RF & EMI emanating from the power supply.
Another thing i've seen is that newer power amp & preamp designs use local capacitance to filter out ripple & RF transients. You see this in many  preamps once you take the lid off - a huge array of smaller computer grade filters on the preamp board (or amp board). This local filtering makes the active circuit less sensitive to RF.
Designers use a lot of metal shielding to compartmentalize the power supply. You see this design approach a lot in Audio Note UK components where there is a metal wall separating the power supply section from the preamp section. When the top lid is screwed down the metal wall makes contact with the bottom & top plates which are grounded. So, any RF/EMI finds a low impedance path to ground via the chassis thereby sparing the preamp section. All these items allow the power supply section to reside in the same chassis as the preamp section thereby allowing a 1-box solution.
Hope this helps. FWIW.   

This fact proves to me the preamp itself is "vastly" superior to it's power supply.When I spoke to Spectral about my experience with my refined AC supply they commented that the unit was designed exquisitely for precision DC output but was not designed as a basic filter for AC, so the better the AC the better the preamp would sound.

Are there components in the PS that would benefit from the latest iterations; or is it possible that the excellence in providing precise DC; when fed by pristine AC; has not changed that much?

I've always held the opinion that the power supply for audio products is the key to their success in sounding their very best.
I'm confounded by Spectral's statement that the DMC20 is designed for precision DC output but Spectral did not pay much attention to its power supply.
For example, I have the best fighter jet for a dog-fight but it has crappy radar. Do you think it will last any amount of time in a dog-fight when we have fire-and-forget missiles?
By Spectral blowing off the DMC20's power supply they've taken their precision preamp active circuit & hacked it at its knees. They've made it immensely sensitive to AC power variations & grunge especially when the DMC20 is a 2-box solution. This does not make any sense. I get the feeling that Spectral does not know how to design power supplies - atleast it did not know back then. Has anything changed on that front today? Don't know....
Of course their power supply would benefit from good power supply design. There are some preamp manuf that use an isolation transformer (like Tice used in his power conditioner back in the early 2000s) that help to isolate the noise on the AC line. I know of other front-end component manuf that use Bybee filters or something similar to filter the AC without constricting the current.
Use of inductive power supplies is well-known for reducing the resulting ripple voltage on the DC supply rails. So, is the use of low-ESR power supply caps. Another well-known technique is local filtering. Separation of power ground from circuit ground that is eventually star-connected at the chassis.
With preamps often consuming currents in the 1A range it is very much conceivable to use a regulated power supply for the preamp this would make the DC power rails superbly stable i.e. excellent load & line regulation.

The manuf of precision DC output is taken to the limit by FM Acoustics of Switzerland (maybe even Goldmund, Soluution, CH Precision & Dartzeel do this but I dont know). That design methodology hasnt changed in that the main tenet is unchanged - precision matching between the channels to get extremely tight tolerances on the output. This of course does not always mean that one uses the lowest tolerance part  - what it means is that if one channel is screwed up (whatever that means) then the other channel is equally screwed up so that the 2 channels match.
Needless to say that when the quality of the raw materials improves the job of the designer becomes less stressful & less tedious. Supplier + manuf are working hand-in-glove to achieve precision output.
Hope this helps.....

Thanks for your feedback ptss.  I don't think i overlooked the built for precision DC output but I agree your original wording gave me the incorrect impression about the DMC20 overall design.
i've heard the previous iteration of your preamp DMC10 - it was better sounding at max gain. The moment my friend reduced the gain by flipping a switch on the rear panel, the sonics went down the gutter.... :(
I went back & re-read my post & it doesn't look like i overlooked if the DMC20 power supply could benefit from latest parts iteration. I believe this point is addressed towards the end of my post & my prev post.
good to read that your efforts to clean up the incoming AC have been very beneficial to you & yes, clean AC power is key - yeah, we agree on that....