Can I use this Dell AC adapter on a different kind of Dell?

If the plug fits, it’s probably okay.

Yes. The 19.5 Volt, 90 Watt, 4.6 Amp DA90PS1 will work on the D6xx series. It will work the docking station if you have one as well as the laptop.
The 19.5 V, 65 Watt, 3.3 Amp is lighter but will only work the PC.

I have dealt with a lot of different makes of computers, both at home and at work, and the Dells are the worst for accepting power adapters from other machines.
Since you are staying in house, you have a better chance of success, but prepare for disappointment. Dells are just that way.

The amperage and wattage ratings on the charger are maximum ratings.

Put another way, if a chair has a 300 pound weight limit, you can weigh under 300 pounds and still use it.

I see it more like engine ratings. Adapter rating is power output capability. Laptop rating is what input power it needs. Like 300 hp for a Honda Civic is ok, but 50 hp engine in a Corvette is not.

So as long as adapter has same voltage and connector, and > or = output wattage you will be ok. Just to be careful see if you can verify the + and – are the same. There should be a diagram on the adapter. Yeah, I’m paranoid.

Update:

I meant to say the charger I’m wondering If I should buy has 19.5V, not 90. That might have thrown some people off.

Alos, has anyone tried this exact thing and seen it work, or is your knowledge just theoretical?

I have plugged all sorts of things into all sorts of other things, sometimes having to rewire things to make them work. I learned to do so long before I went into the Navy and formally studied electrical/electronic engineering further to become an Electricians Mate. I have even built my own power supplies/chargers from scratch.

I like to think I know what I am talking about here ;)