Is version v158 the latest edition of Jessie?
Where to download it?
Which device?
@Carnot
Also the newest version of DietPi still supports Jessie, although we do not offer Jessie images any more, besides for Odroids.
I would also recommend to use a Stretch image, if there is no strong reason for staying with Jessie. Perhaps there is another solution for you than staying with Jessie? Let us know your reasons/issues with Stretch.
If you really need to stay with Jessie, start with a base Debian/Raspbian Jessie image for your device and then use our image creation/preparation script to turn it into DietPi. During this process you can choose whether to stay on current distro version or upgrade to Stretch or even Buster (testing).
Yes for further help, the device you use would be good to know. Install a slim working Debian/Raspbian based image on it and run the following script: https://github.com/Fourdee/DietPi/blob/dev/PREP_SYSTEM_FOR_DIETPI.sh
Raspberry 3B
I have tried to intall the newest version for 2 times, but failed to connect to WIFI.
I have the version v150, which is esaier to use.
It looks like that the version v158 is the latest version of jessie, the “dietpi.txt” may same as version v150.
RPi 3B onboard WiFi chipset BCM43438 wireless LAN , with only 2.4 GHz support and Bluetooth 4.0 Low Energy (BLE)?
If so, it should work. If this will not work, please open a github ticket to get more investigation .
If it is a external USB WiFi stick, we need more information (chipset, USB PID, VID, REV, …)
This is the last RPI v.15x Debian Jessie image. No support, no fixes and updates by DietPi any more, only security updates by Debian via apt-get until mid 2020. Sorry.
For RPi? No.
But I personally don’t think RPi Debian Stretch will cause your Wifi problem.
Where is as well DietPi_v6.0_RPi-ARMv6-Jessie.img, but a little bit outdated.
It will install a lot of updates and patches on the first run. And we will not build a new updated basic image any more.
If you need a newer one, please build your own, see @MichaIng nice distribution. ( thanks for this and the great and easy working script! 
)
Why where is a DietPi_v6.0_RPi-ARMv6-Jessie.img ?
DietPi RPi Stretch build start about one ago. RPi Stretch status
But most people don’t notice, read, or follow this up.
Where are as well some “special” RPi builds, e.g. for AMIBerry or Allo, who take a little bit more time, to get it up and running with Debian Stretch as base.
At the moment @Fourdee work on a AMIBerry image to get it up and running under RPi Stretch. When DietPi RPi Jessie will be history.
Thank you very much.
I will try Stretch again.