New battery will not charge Dell XPS 9550

The reason this is an issue is when the BIOS detects it's a 3rd party pack, it shuts down the charging side until you disconnect the battery and reconnect it. The other issue at play is the clone packs cannot rip Dell's authentication code and brand identifier (DELL) 1:1 due to legal issues. They used to use off-the-shelf parts in the D series and after a few years the clone packs figured out how to trick the old Dells like the D630 while they were in their prime, and they just work if you need a working battery for a D630 because they got it years ago. After they stopped selling them years after their prime, the clone packs for a few of the early E series units (like the E6400/10) were figured out as well. However, Dell began using a custom chip with the E6X20/E5X20 so the laptops can tell and it's harder to beat (as well as a challenge code, basically) now.

Nowadays with Dell, it's decrypted by the time when the laptop is past its mainstream prime since they're just too old to recommend for most people (likewise I would say yes to a cheap E6410 or even an E6510, especially with Quadro graphics, the hard drives are a PITA to replace when they get destroyed before the laptops get sold because SATA III was added to the 5/6X20, but it's still workable). The new (DMCA-safe) solution to the problem is to hide the battery from the BIOS and hope it accepts it — not all of them are. It creates a false positive in ePSA, but "cloaking" is less messy from a legal perspective.
Note: I don't think the 5X00/6X00/10 use custom parts -- those were "decrypted" (and the challenge code beaten) WAY too easily compared to these newer Dells we keep seeing this issue with. This is not news -- the clone packs just have NEVER, ever been reliable after that, so that's why I think the 6X20 uses a custom chip. The reason Dell hasn't tried to block the good clones with the 5/6X00/10 series is the laptops are basically dead to normal users.

Unless you have an original reset Dell controller or the battery vendor ripped the code off of an OEM battery and burns it to a chip that's identical outside of one or two non-critical areas, you will run into this issue on most Dell laptops.