I have a Seasonic in my current rig. Offhand I don't know all of the PSUs that are rebranded Seasonics but off the top of my head I believe Corsair is at least one of them.
Finding out who actually makes a certain PSU can be tricky. Corsairs have been made by Channel Well, Chicony and Flextronics - and Seasonic. The manufacturer can change even within a certain model series, I remember reading a review about one whose lowest and highest wattage models were made by a more reputable manufacturer than the models in between.
The UL number which usually begins with an "E" followed by a string of numbers and is located below a logo looking like a mirrored
UR can reveal the secret. There's also lists and databases about brands, models and manufacturers but for what I've found they're from 2014 or earlier.