kalali A good power conditioner will/should have no voltage drop with a high wattage hairdryer running with everything else plugged into it.
This is completely mistaken.
For one thing, it depends on the rating of the power conditioner. Many good power conditioners are intended for low current use. They simply aren’t designed to be used with "a high wattage hairdryer running with everything else plugged into it."
Moreover, a power conditioner can’t generate current. And it’s very common for sudden high-current demands to cause voltage drop - that’s a function of the service you’re receiving from the electric utility as well as other factors, such as the quality of connections in your service panel and your house wiring itself.
Some people assume that if they have "200 amp service" that the utility can deliver 200 amps, but nothing could be further from the truth. It means only that the service panel can safely distribute 200A. In practice, it’s common for the total available instantaneous current to be much less than the rating of the service panel itself.