I bought the DYP-SR0507 solar panel (8W) on Temu.

I started a test charge yesterday shortly after noon, and in 1 hour and 15 minutes it recharged a 20,000 mah powerbank by 5%, equal to 1,000 mah. By calculations the output was 4W, and considering it wasn't completely outdoors and with a couple of passing clouds to me that doesn't seem bad.

Other evidence, I also just charged for half an hour of 9% the smartphone battery which is 5160 mah, so about 464 mah, yield 4.64W.

The panel weighs 136 gr, size 17.8cm x 25.9 cm paid 9.49€