On the periphery of exotic upgrades is the external power supply. Sometimes this supply is bigger and more powerful than what's standard inside products, but more often than not it's simply the only means of powering a product. A wall wart is a great example.
In my experience, the first use of an external power supply came from PS Audio, nearly 50 years ago (though likely others did it too).
When Stan and I were working on building new products, Stan had discovered the benefits of an oversized power supply: more slam, openness, greater solidity in the bottom end, and far better transparency. The bigger the transformer the better the sound.
At the time, we only made line-level products like preamps and control centers. These types of products were always housed in 1U, 2U, or sometimes a 3U chassis (a "U" is short for Rack Unit and is a standard for rack mounting at 1.75" tall). Our 2U chassis height could never accommodate a monster power transformer so we did what anyone trying to shoehorn in a 5-pound hunk into a one-pound bag: we put it in a new and larger housing. We called it the HCPS for High Current Power Supply.
The benefits from externalizing the power transformer were many: better sound, lower hum, and the ability for our customers to choose what level of performance they could afford. The last one we produced was back in the PCA2 preamp days of the 2000s, as well as a smattering in the Gain Cell line of products. It was (and is) a cool idea but, alas, limited in its appeal.
Seems the trend today is less rather than more.
Big external boxes powering high-end audio products are rare and often viewed more as exotic than standard.
