Can you use a regular coffee maker, and just add a lot more coffee grounds to make coffee as strong as espresso?

It would not work, the water does not stay in contact with the grounds long enough to get all the soluble coffee out like that, without high pressures.

The way to make really strong coffee without an espresso machine is to use a jug or "french press", put several measures of coffee in and add water that is just off the boil.

Then let is stand for at least 15 minutes, stirring every three or four minutes.

Then either use the press to separate the grounds or let is settle & pour off the coffee (or pour through a filter).

I occasionally make a jugfull like that, using ten measures of coffee in a litre jug.

It's not quite espresso but very close...

If the coffee tastes bitter, add a *tiny* amount of salt, a fraction of a pinch.

If you taste salt you have added too much - but a trace takes away any bitter aftertaste & makes it smooth.

You'll just make really strong coffee

Nope, it just doesn't work that way.

Coffee is made by dripping hot water onto coffee grounds. You can grind them finer to get a little more flavor, but ultimately you are using the coffee a bit like a filter, and pouring water through them.

Espresso works by forcing steam through the grounds at high pressure. This extracts a lot more out of the grounds. Water is boiled and the steam goes through the espresso maker, into compressed fine grounds in the "puck" that then turns back to liquid as it comes out of the espresso machine. You need a good machine to do this, but due to the extraction technique here a home coffee maker will never get as much extraction (even if you add a lot more grounds). Good luck!

Espresso is made by forcing steam through the grounds. You can't make it with a regular coffee maker.

Espresso is more than just strong coffee.  It has to be extracted at a specific temperature and pressure.  If you just make coffee really strong it tastes horrible.