A lower US dollar is, in theory, positive for the US equity market. It favors multinational corporations reporting profits in stronger currencies in terms of relatively weak US dollars.

To be more specific, it may be good for their profits and share prices...reported in US dollars. But the dollars themselves are smaller, so it doesn't really mean it's good for the equity market. One share of company XYZ might rise in price from $100 to $120, but might still buy the same number of European widgets or the same fraction of an iPhone, so the share price isn't really higher. If you use the metric of "what are these equities worth in terms of global purchasing power they can generate in future", it isn't that simple. It might be a wash, or even a detriment.

For any given company it probably depends most on the currency mix of their cost profile and of their revenues, including how that cost profile itself will be affected by the currency move. If the US dollar falls a lot, those folks building Caterpillar earth moving machines for export are only paid in shrinking US dollars (great for margins), but they will be hit with inflation and be demanding raises (bad for margins) and of course any imported parts will become more expensive measured in US dollars even before tariffs (also bad for margins).

The large company most famous for doing well from a falling US dollar is Coke, because of the huge exports and the cost profile both tiny and US-based for creating the product.

Jim