Given that the SMC reset didn’t work, possible causes/solutions:
1) Battery is old & on the way out. How old is the laptop? Has the battery been replaced before (especially with 3rd party battery?) New batteries are not that expensive from Apple. You can probably get it replaced via post which may be more convenient than going to an Apple Store.
2) USB cable(s) damaged. I’ve had this before with cheap 3rd party cables. Try a genuine Apple cable which you know for a fact works (ideally someone elses)
3) Something is broken on the logic board (which will need replacing).