Samsung YP-K5J

Tell us more. I looked at those small speakers and thought it probably sounds awful (like the Sony ICF-SW1000). Then I looked at some reviews from back in 2007 on Amazon and people were full of praise for these.

I found this one on a local auction site at a very small price (something like 10 euros) and decided to buy it despite it did not come with a cable (which has a proprietary connector).
It was dead when I received it, so proceeded with complete disassembly and cleaning. The internal lithium battery was charged on a bench power supply and to my surprise it did still hold a charge.
It's a standard rectangular one (fitted between the 2 speakers), so even if it fails, replacements can be found.

After charging the battery, I assembled it back and started testing it. Was really surprised how good it sounds, both on its own speakers (which are louder than one might think) and on headphones.
The speakers sound very clear with a good amount of bass until 60-70% of the volume, where distorsion starts to ocurr on bass. This is to be expected due to limited excursion of the speakers cones.
On headphones it sounds even better and has plenty of power. With IEMs one would never need to crank the volume up to 100%. After using it for some time, noticed that the battery still holds a good amount of charge, as the device can be used a couple of hours at a relatively high volume.
Recently received the USB cable from AliExpress, so started using it more. I'd say it's comparable to a more modern DAP, with only downside being it doesn't play .flac files.