Bear spray does work on cougars and game wardens and national parks and wildlife officials usually recommend carrying some bear spray or even pepper spray when in places that have cougars.
I've read of a story where a man did ward off a cougar who was trying to attack him using bear spray and it worked.
So from that the bear spray did work on that cougar.
However it's best to avoid coming into contact with the cougar if possible but if you need to use bear spray then use it on the cougar.
Although the good news is that cougar attacks on humans is rare as most cougars will avoid humans and don't prey on them.
Cougars do not hunt humans like they do for other prey for their food.
Attacks on humans from cougars can and do happen sometimes but it's also very rare that a cougar attacks a human.
Most cougars will leave the humans alone unless the cougar feels threatened by the human or humans.
Otherwise most times a cougar may just look at you and take off.
Cougars mostly prey on deer, coyotes, porcupines, and raccoons for their food and will leave most humans alone.
A human is not on the cougars prey list but they can and will attack humans if needed.
I've been around cougars when camping and the cougars just looked at me and then went on it's way.