Back in the late 1980s, a friend of mine and I bought a couple of Bentley AT computers (and we received a slight discount for buying what I recall was about $4500 of blazingly fast desktop hardware).
What was a Bentley AT? It was one of many off-brand IBM AT clones available at the time--but with the extra virtue of being a 10 MHz processor with 1 MB of RAM! (Yes, that's MB, not GB.) At work, we had genuine IBM ATs, and they would only run at 6 MHz, so for a couple of months, when I was just started coding on a project, I worked at home--I had better hardware there. (I can't seem to find any pictures of this computer. I guess that they were here and gone very quickly.)
This was my first computer with a real genuine sound card in it (back when those were still slightly unusual), and it included a couple of Labtec CS-150 speakers. (Yes, like these!) Powered only by the output of the sound card, they produced adequate sound, but you could either put a couple of C cells in each speaker, or plug in a 6VDC power supply if you wanted. My fellow Bentley buyer was a bit smarter than me (he's now a hectamilionaire), and rather than have the speakers eat batteries, he went out and bought a 6VDC power supply.
Well, I still have those speakers, and they still work. I needed something a bit louder for a Bible study, so I dug around until I found some C cells, and put them in. They aren't exactly spectacular on sound quality, but they are adequate, and I've had them more than 20 years and they still work.
But they still eat batteries unless I remember to turn off the switch on the back. (Yes, the switch on the left in this image.) I went to Radio Shack to find a 6VDC power supply, figuring, "How expensive can they be?" The answer is: about as expensive as buying a 6VDC power supply with a couple of nice new speakers--some Gigaware 2.0 Multimedia Speakers. They were about $21--and the power supplies were about $23. They look better, they sound way better, and they are louder, too! I suppose that if I had spent the time hunting online, I could have found something equivalent for less money, but there comes a point where it just isn't worth the effort to save $5.