Differences between the 20JF000DUS & the 20JF000HUS laptops

Is that the only difference or are there other differences?

That is the Only difference.

The difference between an IPS display and an OLED display (same WQHD resolution of 2560 x 1440 pixels) can be about 300 Euro (~$330) more.

OLED is just more expensive, but it will have higher contrast, be brighter and be darker than LED.  You can also potentially use less power if you use more darker backgrounds, but you could also potetntially use more power if you're constantly using white or brighter backgrounds.

OLEDs use less power than LEDs.
The only problem is lower lifetime for the existing OLED technology compared with LED.
If 300$ does not count for let's say warranty time of the laptop +1 or 2 years more, then go with OLED, is a lot better. I just hope will come in the near future an improvement in the lifetime expectancy.

OLEDs use less power than LEDs.

That's not true.  OLEDs depend on the black pixels being turned off to achieve the power savings.  When you have the pixels turned up full, the OLED panel will use more energy.   The main advantage of OLED is the larger dynamic range, contrast, brightness, and darkness.  The brightness is akin to what Cathode ray tubes had before LCD screens took over.

You will only save power if you turn the overall brightness down and use your laptop in a darker room or use dark backgrounds.  If you keep it bright all the time, the OLED will use more energy and reduce your battery time.  If you keep it darker all the time, then you will save energy, but that depends on how bright you keep the display.  If you mostly use dark backgrounds, then get the OLED to save energy.  If you mostly use lighter backgrounds, then you will run down the battery much faster with OLEDs.  Default Windows settings include bright backgrounds and many webpages use black text on white backgrounds.  EE is espceially annoying in this regard, but they've since toned it down a very slight bit, but it is still very bright.

http://www.rtings.com/tv/learn/led-oled-power-consumption-and-electricity-cost
https://www.cnet.com/how-to/led-lcd-vs-oled/

LCD panels are really energy efficient.  It's the backlight that uses the bulk of the energy.  They did get more energy efficient when the moved to LED backlights from Cold Cathode fluorescent tubes, but the LEDs still use quite a bit of energy compared to the LCD portion of the display.  At the smaller panel sizes, LCD panels use much fewer LEDs and are much more energy efficient.  As the size increases, the number of LEDs needed for the backlight starts approaching the energy usage of the OLED panel.

If you need to be untethered for longer periods, then get the LCD screen.  If you watch a lot of movies, then get the OLED screen, but be aware that you will have less battery time, unless you pay attention to setting your background darker and remembering to invert the screen colors(Accessibility panel) at appropriate times.

You are right.
I made my statement based on small OLED displays, mostly mono or bi color that I use in small embedded electronics projects and I compared with similar LCD displays having LED illumination background. In such case OLEDs are in the most of the cases lower consumption than LCD, I measured them by myself. But when comes to laptops/TV it really depends what is on the screen, what do you watch, then OLEDs draw more current when all pixels are activated and the laptop battery is empty sooner.