Which RAM sticks for XPS 15 (9520)

A matched pair of RAM sticks is best.  DDR5 RAM seems more finnicky that earlier types. Sometimes a seemingly-compatible stick won't play nicely with other RAM.

Crucial is guaranteed compatible. Here are RAM sticks Crucial guarantees to work with your system. Some have higher frequency than the spec for your system (4800), so those might downclock to 4800 anyway.

Kingston Fury is meant for gaming and higher-performance systems. It has more aggressive timing that may not work in your system.

Some members here have been happy with Timetec. I recently bought a relatively unknown brand, Kuesuny, through Amazon for much less than the price of a big brand name, and I'm happy with it. I ran memory tests for a couple of days to thoroughly test the RAM when I first installed it. It performs well and saved me money.

Make sure any RAM that you buy has a decent return policy.

Dell's Service Manual shows how to remove and install your RAM.

Whenever touching components or working inside a computer, wear a grounded wrist strap, also called anti-static wrist strap, ESD wrist strap, or ground bracelet. It's a cheap and sensible precaution. Rest the laptop on an anti-static mat or at least a reasonable alternative such as corrugated cardboard.

I want to learn specifically about single and dual rank modules. Do they make a difference in 9520 and which dual rank modules are confirmed to work with 9520.

From what I've read, in your system it may not be a material difference so you could choose either. Just ensure to get a matched pair of identical RAM sticks.

So i've installed Crucial 4800 2x16GB 1Rx8

Read speed (measured by AIDA64) is a bit better. now ~66567MB/s, before 63114MB/s, latency similar 93-100ns

Other benchmarks (cinebench, 7zip) don't show any improvements.