My first Solar Watch Charger (SWC) was a cheap, plastic, watch box that I stuck a 12v LED in the top of. I wired it to a 12v adapter.
Later I built a few others, timers, batteries so I could travel with them, etc. I worked with a timer on You Tube and in the post I discussed using it for an SWC. (https://www.youtube.com/watch?v=j0eLz5n58lo) Don't watch the video if you are looking for a solar watch charger, I don't show it being used for that, although, I am currently using it for that purpose.
I actually hooked it up to an aquarium light I bought off of eBay. I used to have the light plugged into a regular timer, the "geek" timer is just because I like messing with stuff. I used those double sided tapes they use for those hooks that can be removed from walls to attach the light to the side of the jewelery box.
I broke the aquarium light clamp because the clamp was designed to fit on a wall thinner than the wooden toolbox I use as a jewelery box. I leave the top open, but, I could wire lights into the lid so I could close it, I just haven't done that yet. (comma splice) The light comes on for about an hour a day to keep my solar watches charged.
There is a guy who took my idea, ran with it and built a really hokey device. He used to sell it for $10 bucks, then more, now it runs almost $30 on Amazon. People have built lights in watch boxes. All pretty simple stuff anyone can do really cheap.
The easiest way to charge a watch is to just set it somewhere and put an LED flashlight on top of it. Just buy a cheap, short, LED flashlight, turn it on and put it on top of the dial. Leave it for a while. Yeah, sometimes the flashlight falls over, but, anyone can prop it up. This is the main reason I couldn't get funding, everyone wanted to know why anyone would buy something they could do with a $1 flashlight.
There are these LED puck lights, buy one at a dollar store, put it under a shelf and shove your solar watch under the light. Easy Peasy. Costco sells LED Puck lights that have a timer built in and a very cool remote. I had to wire a wireless remote into my timer to turn the lights on and off.
There are hundreds of ways to solve this solar watch charging problem. I've shown a few here and discussed another. I like building stuff.
Still, I imagine people will be producing SWC systems into the future. Any of us who own more than one watch needs a way to keep our watches charged. I like the aquarium light best, so far. I can keep 8 watches fully charged in my jewelry box pretty easily.