Not to defend US power plugs (the UK plug is clearly superior) but this sounds like a problem with your adapter. US plugs rely on the socket having enough friction to hold the plug. It's obviously not the best design decision, but I've only had issues with cheap adapters and >50 year old sockets (which are hard to find because they tend to get replaced during remodeling).

The sparks are also less of an issue with 110v.