I keep hearing about 'power dressing' and not really sure what it is

It's a thing for salads I think.
Like when you just pour the salad dressing onto it in a violent fashion to assert your dominance over the rest of the salad eaters.

Unless it's not been reinvented with a totally different meaning, it applied to women's business clothes in the mid to late 1980s. Think "Dallas" and "Die-Nasty" - fitted jackets with impossibly high shoulder-pads etc

80's business fashion was the start of power dressing, using brands and styles to assert you're at the topping of pyramid, the head honcho, that you mean business and that they're not worth your time:

I believe either sex can 'power dress'.....or sexes or whatever

I thought it meant wearing a red necktie.

ironman suit.