If you want a beast amp to drive anything there is this
Ferrum OOR Analogue Headphone Amplifier
OOR, the only headphone amplifier with a soul OOR fully Balanced analogue headphone amplifier Proprietary discrete power amp technology Proprietary 4-pin Ferrum connector for HYPSOS Balanced 4-pin XLR and unbalanced RCA headphone outputs OOR will redefine the category of headphone amplifiers...audio46.com
1.6 watts 300ohm, insane 8 watts 60ohm. God knows how much in 32ohm.
We beat this horse dead already!
In regards to those external PSUs, you are correct that many of them are snake oil. In some cases they will improve the power handling of the amp which could provide some situational performance with headphones that need to swing atypical amounts of voltage, but in many cases have trade offs. Most modern headphones simply just don't have these power requirements except for a few outliers. The Ferrum OOR and Hypsos you mentioned for example have been measured by goldensound (https://goldensound.audio/2021/10/27/ferrum-oor-and-hypsos-measurements/) and the sonic performance actually goes -down- when using the expensive external PSU in some cases like with low impedance headphones/iems.