Also make sure that your plug is fully seated into the outlet, as well as the adapter being fully seated in the UMC. Sometimes when new it takes more effort to seat both.
Best one to get. You'll also need a new wall plate to fit this. It is larger than the cheaper outlets, and thus need a larger opening faceplate.
I've got the cooper now which has the larger size plate. I bought the leviton stainless plate. Although a previous contractor stripped all the screws in the outlet, so the plate isn't held by much.
Only the 9303 shows up on Hubbell's site using their official search. the 9303 is actually Bryant branded.
In terms of quality presumably both would be good as they are both considered industrial style outlets.
If you decide to get one, make sure it handles the torque amount you want it for. I was able to use my torque screwdriver for the circuit breaker of the 14-50 circuit I installed but not the receptacle itself. My screwdriver goes up to 65 in·lb but the Bryant 14-50 receptacle required 75 in·lb. So, for the receptacle I had to use my 25-250 in·lb ("click" type) ratchet torque wrench.
Even though code calls for a torque screwdriver even for screw terminals on outlets, I've never seen a electrician use one. What they usually do is make sure the wire is in all the way (make sure to strip enough for this), tighten, wiggle/tug on wire to make sure it doesn't come out, and tighten again. Some wrap it around the screw with pliers for more contact, but if this is done make sure the wire does not overlap or it will not be a flat surface and may not be able to be properly clamped. Also some terminals are not directly screws, but have a clamp that the screw tightens, so wraparound may not be appropriate for those (given the clamps are typically designed for a straight in wire).
Interesting... so if you want the clamp-down wire connections, it may be worth paying the Hubbell / Bryant premium for 14-50 or 14-30 outlets, but not other outlets like 6-50 or 10-30 since those Hubbell / Bryant outlets have screw-down wire connections like most others (although it is best to choose non-Leviton outlets for -50 and probably -30 based on the plug blade contacts).
Do you still need to use it for a dryer though? If not, then it wouldn't really need to stay as a 10-30. I get why you are saying it can't go to 14-30 if you don't have the extra wire that a 14-30 would require, but the substitute for a 240V only outlet that an EV charging connection would need is a 6-30. It is only three wires and is just Hot1, Hot2, and ground, and you could switch to that from the wire that the 10-30 already has there.
Except there is no UMC adapter for 6-30. There is a 10-30 adapter.
