Green’s Dictionary of Slang

tin-pot adj.

also tin, tinned pot, tin-pan
[note naut. jargon tin-potter, an idler, one who shirks their duties by claiming to be ill. The use of tin-pot as cheap, inferior is SE]

[mid-19C+] of a place, small, insignificant; of a person, mediocre, second-rate; of an event, irrelevant.