To test flash powder compared to electronic flash, I shot the same scene lit with my Nikon SB-28 flash, my Novatron studio flash, and a few grams of flash powder. The results are quite remarkable. Powder flash can be REALLY bright.
This image requires some explantion. It's a contact print of a strip of 35mm film. There are four frames in the filmstrip. From left to right, we have Nikon flash, a "dud" frame which is to be ignored, then the Novatron (you can see the back of the Novatron head in the picture), then the powder flash.
The same strip of film was contact-printed twice. The top exposure was made for the flash powder, which makes the frames shot with electronic flash completely dark. The lower exposure was tuned for the electronic flashes, and shows the powder flash completely white. Given the latitute of photographic paper I would say that the powder flash exposure must be at least 6 or 8 stops brighter (70 to 250 times brighter) than the Novatron.
This was not an extra-large pile of flash powder. If you want more brightness, you can just use more. It's cheap.
Also, flash powder is extremely dangerous and should never be used by anyone.