I think you need a 4th option: works sometimes, fails silently sometimes, other times fails obviously, fire always possible

What application do you think you have for this safety hazard? There's almost certainly a better way.

@Ecnerwal I don't; just browsing. The question (from me) is entirely hypothetical -- I like my house too much to burn it down.

Not UL listed, The receptacles are too big, should only be for 15 amps, trying to use 30 or 50 amps will trip the breaker. Best to use a UL listed on a proper MWBC.

What is it for? There are a lot of significant dangers. You would think there is some application where the risks can be mitigated or accepted. But I cannot think of one. So it's just dangerous for nothing? Why make it then?

This may be intended for a hack to power a RV from a generator lacking a 30amp outlet.

I have seen a version of this device made in USA, with appropriate circuit breakers and safety interlocks to prevent energizing it without both plugs verified to be plugged into opposite phases. I still doubt it's legal but it seems a lot safer.

Hmmm, If 1 120 circuit breaker trips, usually we want both sides to trip. This cord will not ensure that.

Why is it legal for Amazon to sell such a dangerous piece of equipment? Based on the voltage and the connector, I assume you are somewhere in the USA, Canada, Mexico, Japan, or Central America / parts of South America? When I view the website from Germany, no price is listed and I suppose they can't sell it here (in case someone thinks it's useful for travelling...). Where are you that this is legal/approved?

@mikes there is no generator that produces split phase 240V, does not have a240V outlet, but does have 120V ones on both phases. Why would anyone make that?

Is it so if you have an RV and you visit a friend you can use their power with two long extension cords and maybe burn down their house or electrocute their family but hey why didn't they just let you sleep inside?

@jay613 As for "why would anyone make a split-phase generator without a 240V outlet", the answer could be "product segmentation": design one generator, sell a cheaper version without 240V and a more expensive version with a 240V outlet. Get two products on the market for the price of one and profit! Yes, sounds crazy, but it is done at a staggering scale in all sorts of fields.

@gerrit amazon get away with selling all sorts of stuff that's not approved and even outright illegal by being in a some sense "not the seller" - they claim to be a marketplace, even if the stuff is in their warehouse and they get most of the profit. But it's now got me wondering whether the complete absence of reviews means none of its users survived

@TooTea and then someone comes along with a "solution" that's far more risky than modifying the generator to add the missing socket

@gerrit From a legal perspective, Amazon isn't selling this. Some merchant which calls itself "numberds" is selling it. Amazon is merely offering the website on which you buy it, taking your payment, and shipping the item to you. Now, to me, that sounds a whole lot like selling it, but I'm not the one who decides what legally counts as "selling" and what doesn't.

@TannerSwett Maybe my local supermarket is not selling me any chocolate, they're just providing the shelve space, taking the payment, and providing me with the chocolate, but it's actually sold by some confectionery company ;-)

If you have an amazon account, you can go and report it as unsafe. Get this thing removed before it kills someone!

If it were an adapter to one of the European 220V house plugs it would make sense. Need the higher voltage, but still running small appliances, so not going to need too many amps. But for US appliances, if it's running on 220V it probably needs way more juice than two dinky 15A circuits can provide when wired up this way...

@Tristan Thanks for the suggestion, I just reported it as unsafe.

can't the USA just transition to 240V and never have to deal with this sort of non-sense?

See also this question on Electrical Engineering SE: electronics.stackexchange.com/questions/681125/…