Without pics, I'm guessing tolerance issues.
Maybe you can reshape the hook of the jack to better catch the plug-tip's indent?
I've had sub-standard jacks that didn't match up with higher quality cable-plugs and vice-versa.
For another example:
When I buy a tyre for my MTB, the standard I adhere to is a 26"-RIM, so I buy tyres that should fit that size rim, but...
One tyre brand, the rubber goes on the rim easily and after getting a flat, I can remove the tyre from the wheel with my bare hands and fix the flat.
Another tyre type or brand can be a total bitch to install, the bead tighter than a chastity belt during the crusades and thus breaking many plastic tyre-levers and nearly breaking my fingers in the process of getting it on. Get a flat out on the trail? Good luck changing it!!
Some rims are just that teensy bit bigger than they should be, while some tyre-beads are that teensy-bit tighter than they should be — pair the two together and ... @#$%^&* IT!
I don't care how much grip the tyre has on the trail, how well it works on the wheel — if I try a new tyre and it's a PITA to mount and unmount on the wheel I don't waste effort or time anymore — just move on to what's tried and true to my set of wheels; give the tight'n' to someone else and let them fight with it, or if they're lucky it works easily on their rims.
Anyway, back to jacks. Unlike the jacks / plugs that had tolerance issues with each other — I once bought some jacks for an amp build that were only jack-shaped objects. The metal was so soft that after plugging in once or twice the jacks refused to make proper contact. Caused a lot of headaches diagnosing that because I'd fix them — bend them into place so they'd make good contact — only to have them not working within minutes of checking by plugging/unplugging a couple of times.
So now I've got this bag full of Jack-shaped objects that are useless unless I can turn them into jewellery or keychains.
Expensive lesson learned, that great deal isn't so great if what you buy is crap — as the adage goes:
some things you've just gotta buy once, cry once.
