The U12S is a very nice and quiet cooler but it's not ideal for a 3950X working 100% 24/7 if you're going to sit near it. It keeps up with a 3600 or 5600X just fine, but to work with a 3950X I'd say you'd need to add an extra fan and that costs so much that I think you'd be better off with a bigger tower cooler like the NH-D15S, NH-U14S or the Scythe Fuma 2. Gamers Nexus has done some air cooler reviews recently, and TechPowerUp has detailed CPU cooler reviews too.
Link to Noctua's compatibility chart for the 3950X: https://ncc.noctua.at/cpus/model/AMD-Ryzen-9-3950X-1035
Of course these considerations are mainly for gamers and home office use - if your PC is a pure folding rig, you might just increase the fan speeds a bit and get similar performance with a bit more noise.
Edit: A correction
18401 - Optout
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Re: 18401 - Optout
Last edited by gunnarre on Thu Sep 30, 2021 12:06 pm, edited 1 time in total.
Online: GTX 1660 Super + occasional CPU folding in the cold.
Offline: Radeon HD 7770, GTX 1050 Ti 4G OC, RX580
Re: 18401 - Optout
I updated my previous update (listing the model of my existing cooler on that 3950X).... A new case is on the upgrades list too (a Cooler Master HAF XB EVO unit).
Paul
Paul