If you need a cheap USB charger for some older phone or a device that doesn’t require much power, the dollar store chargers are a practical option. If you need to charge the latest tablets or smartphones, that won’t work so well.
They simply don’t have enough power to charge modern devices. Even if they manage to charge them, it will be painfully slow. If your battery goes completely empty, they won’t have enough power to jump-start the charging process. That initial “kick” requires a lot of energy. If you are thinking about buying just the USB cable, the wires inside are so thin that they can’t conduct enough electricity.