Are you sure it isn't mealy bug? This is one of the most commonly misdiagnosed insects on houseplants and garden plants. The white fuzzy blobs on your houseplant leaves surely look like a fungus, but in fact are not a fungus  they are an insect. When I first came across this on my oleander, I thought it was a fungus. Alas, it was not.

Here is a link that might be useful: mealy bug info.

Spray with milk from a spray bottle. There is something in milk that destroys the powder mildew. Google it for more info. I had several shrubs with bad powder mildew and the milk helped.

Barb