On my AM4-mainboard, the best collection of temperature sensors is at /sys/class/hwmon/hwmon[0-4]/temp[1-9]_input
This does not include the GPU, which gkrellm covers.

an SSD is basically a very large USB stick

More like several "USB stick"s in RAID0, with dedicated DRAM cache (or host RAM cache if you're a cheapskate) and a far more intelligent controller.

Usually, though what it's called varies by manufacturer.

Assuming it reads data from the usual sources, I don't see why not. Honestly I have no idea why people want some dedicated tool like hddtemp just to print data already available in sysfs or via smartmontools.

The only accurate  way to compare is, as always, to stop obsessing over manufacturer specifications and actually measure power consumption under your specific workload.

SSDs generally draw peak power under sustained write workloads, HDDs at spinup / spindle start.
The big power saving from SSDs comes from write-heavy workloads being intermittent, idle power draw being very low, and the transition being practically free.

With a HDD you have to choose between keeping the spindle running all the time (thus higher idle draw), or starting it only when needed (incurring access delays and spikes to near peak current).
For laptops there's the added complication of a spinning drive (i.e. unparked heads) being vulnerable to physical shock, so they usually run very short spindown timeouts - that's great for power consumption if the drive is usually idle, but terrible if it has to spin back up every other minute.

There's also an advantage in SSDs not needing to physically move heads around, so all areas cost the same to access (caching complications aside) and reads can use much less power than writes (typical workloads often being more read than write).
The power consumption of a HDD for a given operation will vary with where it is on disk, i.e. how many seeks and how far, and seeking to a read location uses just as much power as seeking to a write. (upshot: defragging your rust not only makes it faster, it also saves energy )

Again that's peak power, and it's simply because faster drives use more power under load. The bus itself makes very little difference in the real world, because ASPM.

Now you're talking about the 'card' drives that don't even use SATA connectors. Power usage doesn't seem to be linear there, either.

Generally spoken, there is not much difference between SATA SSDs in the typical 2,5" housing and these typical 2280 M2 cards as used for NVME drives. The power consumption on all of them are load frequency dependent.

And as a matter of fact, SSDs are in average of much lower power consumption as the spinning rust drives. Don't look at the rating, this is a max consumption value a drive rarely takes in in very extreme situations (and gets very hot and slows down to protect).

Out of curiosity, I popped the cover on a laptop I have to see the tiny little HD. It's only got a 5v rating, and it's .55 amps. The motor must be running in the 5v feed along with the electronics. So now I'm really questioning whether SSDs are automatically less power hungry than spinning disks.

At least these disks I have already bought are intended for desktops. I just want the faster load times. But if I decide to get SSDs for my laptops, I will be shopping very carefully...

But to be considered: PCIe3 consumes less than PCIe4, less than PCIe5.

But now I have a new thing to check on SSDs. Another brand I got access to, PNY, shows only 1 amp for a 2TB SSD. Quite a difference from the Crucial, and for more storage. Hmm....

o that power calculation doesn't seem to work out for these.

SSD 5v * 1.7a = 8.5w

HDD 5v * .68a = 3.4w, 12v * .55a = 6.6w,  for a total of 3.4w + 6.6w = 11w, it uses both them voltages at the same time internally.

Seems to me the HDD uses more power, then again I know how to do the math.