the only way to reduce weight and size is to increase frequency use SPS). there is just no way around this if you want output to be isolated.
next question is if you want to buy or build or hack existing one. good candidates may be SMPS for audio amps. They tend to provide dual output (+/-35 or 40V). Personally i would go consider hacking 500W PC PowerSupply due low cost, then rewind the secondary, and throw in pot to adjust output voltage. I am using smaller one right now to get 1-25V output and up to 30A (not at the same time). All i did was add potentiometer and output terminals.

I actually had one of these "hacked" as well. It doesn't sound like too bad of an idea, although I've tried rewinding a transformer a couple of times, let's just say it's not my forte. It occurs to me that the same principle of simply connecting several of the 12v lines + 5v + 3.3v in a combination of series and parallel could get me to 80v but I have no clue about the amps. Does that seem possible?

 

no hacking needed:

get some a single big SMPS PSU with single output, for example
https://www.amazon.com/Switching-（SMPS）Monitoring-Industrial-Transformer-220VAC-DC24V/dp/B0786LMNR2/
That will take care of weight and galvanic separation from mains.

Then use it power suitable module to get different output voltage.

To boost voltage try add something like this
https://www.amazon.com/Voltage-Converter-Supply-Module-10-60V/dp/B07N6BJWXH/

To lower voltage get something of this kind:
https://www.amazon.com/Solu-Converter-Step-down-Adjustable-Constant/dp/B00VWLT2KU/

Maybe get the step up converter first to experiment a bit, you can power it from you existing device set to 24V for example (whatever the new PSU is supposed to output). specs and info on this DCDC boost converter are sparse...

so if something goes wrong, you owe me nothing.
if it works out, you owe me case of beer of my choosing.
if you really like it, you owe me two cases.