A GTX 1650 without an external power connector will probably work the best. The HD6670 doesn't use one, either, so it's highly likely that your power supply doesn't have any PCIe connectors and is low wattage, if it's a pre-built and came with that card.
A GTX 1050 Ti, GTX 1050 or GTX 1030 are also viable upgrades, but watch out for GTX 1050 Ti cards that require external power. Some need it, some don't.