And the 285H is lower performance than a 275HX.
Their laptop naming scheme at least is fairly straightforward once you figure it out.
U = Low-TDP, for thin & light devices
H = For higher-performance laptops, e.g. Dell XPS or midrange gaming laptops
HX = Basically the desktop parts stuffed into a laptop form factor, best perf but atrocious power usage even at idle. Only for gaming laptops that aren't meant to be used away from a desk.
And within each series, bigger number is better (or at least not worse - 275HX and 285HX are practically identical).
Don't forget the V series in there. I have an Intel(R) Core(TM) Ultra 7 258V in my Thinkpad. I think they're still being made. I bought an open box Thinkpad T14s Gen 6 with it - they come with a nicer GPU than the Ultra 7 255U.
The V series is a one-off thing Intel did, but they don't have a direct successor planned.
Previously, they had a P series of mobile parts in between the U and H series (Alder Lake and Raptor Lake). Before that, they had a different naming scheme for the U series equivalents (Ice Lake and Tiger Lake). Before that, they had a Y series for even lower power than U series.
So they mix up their branding and segmentation strategy to some extent with almost every generation, but the broad strokes of their segmentation have been reasonably consistent over the past decade.
Very interesting. I was a bit out of the loop on Intel mobile CPUs; I looked up the benchmark specs for it when purchasing and saw that it generally trounces the 255U.
I've been really quite happy with it - most of the time the CPU runs at about 30 deg C, so the fan is entirely off. General workloads (KDE, Vivaldi, Thunderbird, Konsole) puts it at about 5.5 watts of power draw.