The panel charges with too much amperage (theoretically in perfect conditions). I am now looking for a way to get the 300 watts from the panel anyway.

Go.

I have this pad (300W) and the EcoFlow Delta 1300, but I haven't had a chance to test the combination yet. At the moment we are blessed with rain, so I will do so at the next opportunity and let you know again. However, I don't really see any reason why it shouldn't work, the cables supplied fit.