Let me step in here for a minute... the OP has IMO been very gracious in sharing his experience with us for the benefit of everybody in this community. That takes quite a bit of humility and willingness to step up to the plate and "take one for the team" so to speak.
I have discussed this industry wide problem several times and every time there are a couple of members who suggest that I am making this stuff up. Clearly, I'm not as I have helped several members here with this exact issue and not just on our products but on ANY product that uses SpeakOn connectors (including our competitors). This is truly an INDUSTRY problem rather than any single amp/speaker manufacturer problem.
In the case of this particular problem (and a few others recently), the keys on the plug were molded undersize (both in diameter and in width) so that it was quite easy to install the plug backwards (180 degrees off) in the jack. Normally the keyways in the jack would reject this but there wasn't enough meat on the plug's keys to do so. Once the connector got twisted to lock, they got hung up on the machined reveal in the back of the housing and it wouldn't easily find its way back out. The difference in thickness of the key between the genuine plug and the knock-off was about 40%. This brand the OP confirmed was Monoprice (a generic "cable & accessory house"), and has been the source of many of the plugs that we have had to surgically remove from amplifiers. This is both time consuming and costly for us and is also costly and inconvenient for the customers. It is entirely avoidable by insisting on genuine neutrik plugs.
While it might appear that this was a user error, and in part it was, it would not have happened with a genuine plug because that's the entire purpose of the rejection keys (one is wide and the other is narrow). In fact, I tried a genuine plug in his amp just to verify and it would not go in backwards.
I posted a couple months ago about how the contact assemblies on another knockoff plug came apart inside the jack and bent one of the contact fingers back and bent the rest of the contact assembly. This caused what first appeared to be an intermittent, defective amp but in the end was a damaged jack.
This is not unlike the challenges we had years ago with 1/4" plugs that had "unique" tip profiles, some so poorly designed that they would crush the leading edge of the contacts on some jacks. There was also the oversized and undersized plug sleeves that would either get stuck, damage the jack or bend the guts that would then make other plugs intermittent. The rule back then was to stick with Switchcraft and Neutrik plugs!
I hope this information is helpful to everybody here.
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