I have a 300W low voltage transformer for landscape lighting. It has terminal for 2 circuits. Does this usually mean it can handle max 150W each circuit or just a combined 300W (e.g. 200W on Circuit A and 100 W on Circuit B)? It also has a low and a high (as well as a Com) terminal for each circuit. I assume Low + Com = 12V and High + Com = 24V? Or does this have another meaning?

It's an old (4 years old ) Hampton Bay brand and Home Depot cannot find documentation for it.