Will charging at lower wattage increase battery lifespan?

TL;DR No. If you plan to keep your laptop plugged in multiple days/weeks, use the Primarily AC Use setting in the Dell Power Manager software to lengthen your battery lifespan.

The answer to this question would seems to be (wrongfully) yes, because the slower your charge a Lithium battery, the less stress/heat you put on the battery, thus the more lifespan you can expect out of it. But there's more to the story.

The first thing you need to understand is that your laptop only uses the power it needs. The 60W or 130W rating of your charger is only the maximum power it is allowed to draw from that charger (the charger will tell your laptop about this value). But if it only needs 20W to perform its functions, it will only draw 20W from a 130W charger.

Now, to answer your question, no it won't increase the lifespan, because the charging circuitry included inside your laptop is designed to only provide the necessary power to charge the Lithium battery that's inside your laptop as fast as possible, safely, without damaging it by giving it too much power, which is probably somewhere around 15W. So using a 60W or 130W charger won't make a difference here.

Then why does Dell give you a 130W charger if you only need ~15W to charge the battery you ask? That's because it would be very interesting to actually able to use the laptop while it's charging don't you think? A quick google search shows that an XPS 7590's CPU is capable of pulling a maximum of 45W and GPU 50W. Therefore, if you were to use a 60W charger while your were demanding a heavy load on your laptop, it would probably not charge. However, it would charge just as fast as with the 130W charger at idle.

One way to lengthen the cycle lifespan of your battery if you plan to use it a long time (days) while it's plugged in is to use the Dell Power Manager software and configure the battery as "Primarily AC Use". This will stop the charging above ~80%, which will lengthen the battery cycle lifespan, but shorten the daily usage time (you start at 80% instead of 100%).

Hope this help and don't hesitate if you have more questions!

@beachysdan  Building on the information above, using a 130W charger is unlikely to result in faster battery charging than a 60W charger when the system is not actively running, meaning that even when you only have a 60W charger connected, the system likely isn't using all 60W to charge the battery. If you want to verify this, a simple multi-meter like this one that I have will tell you how much power is flowing across a USB-C link at any given time, broken down in voltage, amperage, and resulting wattage.  Using a 60W charger will however make your system very likely to throttle its performance pretty significantly given that you'd be providing less than half the power it's designed to have available.

For what it's worth, the general consensus with Li-ion batteries is that you can charge them to 80% without taking a longevity hit.  Tesla uses that threshold, for example, and it's mentioned on sites that have a lot of helpful information such as Battery University.  Limiting maximum charge even below 80% is unlikely to improve longevity much.

@Tinynja  Does "Primarily AC Use" only impose a maximum charge level of 80% without also specifying a minimum charge level?  If so, then while that option might be an appealing balance of longevity vs. everyday practicality concerns, if you're willing to sacrifice more of the latter to gain more of the former, then the OP's setup of specifying a minimum charge level is even better, because in that case the system won't even attempt to keep the battery topped up to 80%.  It will instead allow the battery to remain idle and self-discharge down to the minimum charge level before providing any more power to it.  If you never actually use the system on battery power during that time, self-discharge can take literally weeks -- so in a setup where you specify both maximum and minimum charge levels, your battery will spend the overwhelming majority of its time completely idle, neither being charged, nor kept topped up to its max charge level, nor actively drained.  I run a max charge of 80% and minimum charge of 50%, for example.

The catch with a minimum charge level of course is that even if you've had your laptop connected to wall power all day, you might end up only having a 50% charge when you disconnect, not an 80% charge.  And that might be why the "Primarily AC Use" built-in option doesn't enable that.