I got both Romoss 10,000 and 20,000 mAh models. After months, I noticed something strange with the bigger model, so I set up a test.
Both power banks had been fully charged. I used a capacitor to draw the power out at the constant rate of 5V 2A. The smaller 10,000 mAh model was completely drained after around 3 hours.
However, the bigger, more expansive and supposedly or having/been advertised to have at least twice capacity of the smaller model was, surprisingly, completely drained after only 2 hours 40 minutes.
They also advertised “12-month warranty and friendly customer service” but it reality it’s totally a hassle dealing with them. They refused to honor the warranty unless I had a video to prove the incident. But Amazon messaging service doesn’t allow attaching a video or even URL. I told them and they didn’t offer alternatives so it’s a deadlock. I decided just to post the video review here instead.