How to secure a large power cord to a piece of equipment?

Plug too loose, wrap it with a layer or two of black duct tape,

Plug too tight, sand/file/shave the plug to fit in fully

Cord too heavy: you need a place to attach a string/twistie/... and carry the cord’s weight. A string or twistie from a screw on the unit, or a nearby heavier unit. a small hook in the rack or windowsill or the wall behind, string tied from hook to cord. Think easy removal.

My Ortofon Phono cord is quite heavy, I support it’s weight via a hook just behind the plinth.

My Cayin power cord is heavy, but it is on a separate cabinet, I am able to simply push the cabinet back just enough that the cord is held in by pressure from the wall behind. I am able to position the amp anywhere front to back on the cabinet to make that work.

I have to admit I would be very concerned in getting a high end power cord that does not fit snuggly. This is one of the characteristics that goes up in high quality power cords. I would return it.

The best sounding power cord I have purchased. Audio Quest Hurricane, is so tight (I have more than one) that it takes a tremendous effort to get off and on. Not because of the outside… but conductor contact. I am sure this is one of the parameters making the cord sound so good. Although all of the high quality cords I have purchased fit snugly at least.

You can check Furutech's NCF Booster, enhancer and cable holder.

If you have the space, put a small wood block between the plug and the shelf below it to raise the plug up a bit. Not very inspiring when this happens. I like my power cords to fit properly.  

A couple of turns of black insulating tape, or self-fusing silicone tape.

Who knows whether to blame the socket or the connector?  The short story is that while there may be a standard, many manufacturers don't adhere precisely to it.  I've had plugs that were loose (e.g. Cardas) and plugs that were tight (e.g. Audio Envy), but that was going into different associated equipment.