Wall Charger + NEMA 14-50 on single circuit?

From a technical stand point there's no reason not to.

From a code stand point.... I can't answer that for your jurisdiction, however I wouldn't expect an issue?

If your inspector would buy the argument that you will only use one at a time, it could pass muster. You will need a box to hold the "T" connection; why not use something like this that will only energize one at a time, and you should not have any problems; it's only $99 from Amazon. Amazon.com : Reliance Controls TCA0606D 60-Amp : Generator Transfer Switches

You don't really need another box, you can splice in an outlet enclosure, so the original 14-50 can also be the splice box.

I don't believe that will be allowed. I'm pretty sure hard wired Electric Vehicle Supply Equipment has to be on its own branch circuit. I also believe that 50A outlets have to be on their own branch circuit.

You could put in a sub-panel and then move both onto it with their own breakers. I'm not sure about the appropriate sizing for that wiring, you might be able to reuse the wiring you have for the NEMA 14-50.

I put in an HPWC and a NEMA 14-50 but they're in different bays in the garage and are on separate circuits.

If you have the switches in the HPWC set to 40A charging, why can't you put a flexible cord and 14-50 plug on it? That would avoid the whole at-the-same-time issue. Just unplug one and plug in another.

The reason you normally can't use a plug on the HPWC is that there is no plug that can handle the full current of a HPWC.

You'd have to check with an electrician, but this almost certainly violates code as these devices are required to each have their own branch circuit. But from a feasibility standpoint, it shouldn't be terribly hard to just splice the existing circuit and add the run to the wall charger. As far as whether you'd be able to do this if you have a switch or breaker that guarantees they can't both be active at the same time- that's a question for an electrician. Maybe someone here happens to know for sure in your area, but you'd probably get an answer faster by calling a local sparky. ;-)

It's a gray area. There is nothing that specifies a dedicated branch circuit unshared with anything else, and even if it did, you could easily get around it by turning the HPWC into a plug-and-cord connected appliance by attaching a NEMA 14-50P cord set on it and plug it in to the very outlet that serves as your backup. Manufacturer's instructions must be followed (art 110) but I don't see any manufacturer instructions that require a fully dedicated branch circuit.

The only governing rule here is that you MAY NOT have the HPWC set for anything greater than a 50A breaker if you share that circuit with a receptacle, because a NEMA 14-50 receptacle is to be installed only on 40A or 50A rated circuits. (You can't install a 100A HPWC and connect a 50A receptacle to the wiring - I say that to be clear because I've been asked.)

Polaris connectors can be used to do this circuit "T" pretty easily; however, unless you're using a large/deep box you may not meet proper box fill requirements if you try to put the junction in the outlet box. You're best using a square project box with cover, placing the junction there, then feeding the HPWC from the side of it.

An inspector might find some other technical reasoning that would disqualify it in their eyes. If your jurisdiction requires inspection, call your local code inspector and ask how they'd approach it.