Would any offence be committed for:
Having this on your person?
Buying or selling this?
Leaving it around for people to plug in to a computer?
In the abstract, I don't think that this conduct would violate either Section 36 of the U.K. law or U.S. law, although, obviously, purposefully destroying a computer itself (i.e. actually using the device without the consent of the owner of the computer) would violate many U.K. laws and would also violate many U.S. laws at both the state and federal level.
I also don't think that possession or buying or selling this product would be a crime absent some intent that it be used illegally, in which case there might be an "attempt" to commit a crime offense, or an offense that would make one part of a conspiracy to commit a crime.
In the "leaving it around" example, there is arguably an intent to use it to harm another improperly, although the phrasing is ambivalent.
While many statutes in the U.S. criminalize possession of burglary tools, or drug paraphernalia, sometimes with an associated intent element (although even these crimes often have an express or judicially implied intent to use element), I'm not aware of any statute that criminalize possession of tools for malicious destruction of property. So, if the tools aren't possessed or used in a manner intended as a step in the facilitation of a crime, I don't think that any law is violated. So far as I know, the U.S. does not have a counterpart to Section 37 of the British statute cited above (it isn't a terribly easy thing to search for to definitively rule out the existence of such a law because federal law has many uncodified crimes in unexpected statutes and there are many sets of state criminal statutes, not all of which are codified either).
The example giving in the comments by @gnasher729 of possession of a hammer which could be used to do the same things that this object could be used to do is instructive.
Arguably, this USB-like tool is more specifically targeted at malicious conduct.
But, for example, when I used to work as a radio news reporter, we had a machine that was basically a high powered magnet that was specifically designed to destroy all information on magnetic media. This was, in part, so that it could be reused, but it was also so that confidential interviews wouldn't fall into the wrong hands once they were no longer needed, in much the way that one might shred paper documents.
It isn't so implausible to think that a device like this one might be necessary for individuals or firms with national defense secrets embedded in their hardware and software to have on hand in order to destroy a sensitive computer in order to prevent a security breach, if necessary.
In a case like that, leaving one of these devices around the office unlabeled might be negligent, but wouldn't have the intent necessary to be an intended crime.
And, it is hard to imagine that the device itself, which seems pretty simple, would itself involve any technology that is a national security secret, so it probably wouldn't violate export control laws.
Of course, possession, purchase or sale of such a specialized device, or leaving it around unlabeled would certainly be powerful evidence of an intent to use the device in a wrongful manner, and hence, of an attempt to commit a crime. Indeed, possession of such a device or purchase of one might very well be sufficient to establish probable cause to seize the device and arrest the person holding it on charges of an attempt to destroy a computer. But, this device would be merely powerful evidence of an intent to commit a crime, rather than something that is a crime to commit in and of itself.
There are no international laws that govern this kind of thing. The only international laws applicable to individuals pertain to war crimes and nuclear and chemical weapons. Even then, most international laws direct member nations to adopt domestic laws on the subject rather than being self-executing.
