Sorry my data froze up for some reason had to re boot phone.
About the dimmer cords. I have a few of the white ones. You plug your uth directly into the back of the dimmer plug. The end of the cords are a slider switch. Even wide open none of them will let any of my heat mats go above 75-78.
So be wary of lamp dimmers some of them are total poo.
Good ol fashioned zoo med analog rheostats are still dirt cheap and reliable.