Can't disable EcoPower

Hi, I have the exact same problem. Brand new Inspiron 5406 2-in-1. Dell has no idea what's going on. Updated device drivers, BIOS. Tried changing settings from power options, Intel graphics command center. Went through remote support. Dell even sent a technician to replace the motherboard and it didn't work. Technician told me they haven't encountered this problem before. Next visit they're gonna try changing the LCD, SSD. Doubt it's gonna fix the problem. Has anyone found a fix?

I am also experiencing this exact issue with the Inspiron 5406. BIOS properly applies changes made to the default brightness of the display, but not EcoPower.

It's the same issue I have been experiencing. Because of ecomode the display flickers when on battery power. I have tried all stuff but it doesnt work. Apparently, I have an assumption where getting back to old bios may enable the old intel graphics panels where we can disable the option. Just like those simple flicker solutions mentioned for recent dell products. If anyone gets lucky please inform.

check my solution!

found the issue and it is resolved now. a wonderful fellow with a github username orev solved this issue in microsoft surface pro. I applied this on my own system and it is working perfectly. 
https://github.com/orev/dpst-control
(Select the green dialog box with code written on it, select the bottom option of Download Zip) 
-------->Click here to download directly (https://github.com/orev/dpst-control/archive/master.zip)
Download the file from here, it will be in zip format, extract it to a folder and then run the disable-dpst.bat as an administrator. it will stop the weird screen flickering behaviour. !!!! One can also check the DPST via running get-status.bat as an admin.
Thank you and You are welcome. You guys made me seek solution and made me feel not alone with this issue. heck the bios. ultimately the goal was to stop screen flickering when using on battery power.

The DPST control solution doesn't work for inspiron 5460 2 in 1. Been there done that. It presumably controls the adaptive brightness for laptops with ambient light sensors (I think, I don't have other laptops).

Ecopower adapts the screen brightness based on screen content. Dark coloured content higher brightness, light coloured content lowers brightness. Nothing to do with ambient light.

And it is horribly annoying when you're switching from a dark coloured content page to a light coloured content page. You get the momentary 'blindness' where nothing on the screen is readable for 1-2 seconds or so. 

Dude you have a 5460 not 5406! There is a difference!!!

Well I suggest you try it. The new bios disabled the option of DPST from intel graphics manager and now it shifted it to bios under combined ecomode option which can only be modified by registery. Try the github solution. It is working perfect for me for now! Even dell seems to agree with it. The bios need to be updated by dell to allow devices to change anything in it. However 1.1.7 does not seem to be an adequate update you or I were waiting for. Btw did you knew that there was no thunderbolt 4 port in it during time of buying. I recently bought it like 2 days ago and the official dell executive said to me that it is thunderbolt 4 port. Now I have talked to dell customer executive online as well as checked on manual, I feel like I got misguided by uninformed shop owner.

Typo error. I have the 5406 2 in 1. 5406
Have already tried the DPST before coming here.

If you have the Intel graphics manager then you're not holding onto the 5406 2 in 1. The only intel graphics software available on 5406 2 in 1 is the intel graphics command center which has no option for adaptive brightness.

Disabling DPST does not affect EcoPower, which is the root cause of the content adaptive brightness issue in the 5406.

May i ask which bios version or firmware version are you both guys on? It will help me narrow solutions for the issue.

Bios 1.17. All updated to latest drivers as well. 

Temporary fix I found:

1. plug in your laptop to the charger 

2. Make sure the brightness doesn't adjust by itself by switching pages/screens. Sometime it's buggy and you may need to unplug and plug in again 

3. Shut down your laptop while plugged in. Wait till it's really off, doesn't hurt to wait ~ 30seconds

4. Unplug the charger.

5. Start up your laptop. It should be running on battery power now.

6. Try switching screens/Pages, brightness shouldn't be adjusting automatically. 

Seems it really is a software bug and they can't even program it properly to detect ac/DC power.

Can anyone confirm if this works for you too? 

BIOS is 1.1.7 and all drivers are up to date as well.

@Schneizel 

This worked for me. Thank you! Let's hope this gets remedied properly soon though.