For credit for AMT, "Adjustments or preferences treated as exclusion items" it says use Form 6251 line 27 but this seems unrelated. Is this the right value?

I am inclined to agree with you. 

Are you seeing an instruction in TurboTax to enter adjustments or preferences treated as exclusion items on line 27 of form 6251? If so, where do you see that instruction please?

I do see this as guidance in TurboTax. Next to the field "Adjustments or preferences treated as exclusion items" there is a "Learn More" link, which directs to the following text: "What can I enter as an exclusion item? If you filed Form 6251 last year and it contained exclusion items on line 27, you can enter the total of these lines here. An exclusion item is permanently nondeductible for AMT purposes, as opposed to a deferral item which will reverse in later years."

I did some research online and it looks like maybe the right thing for me to enter here is last year's standard deduction, which I took ($24,000).  Does that sound like a plausibly correct way to fill out this line item?

I see the same thing tracyg0683 in terms of the info in the  "Learn More" link where it says 

"If you filed Form 6251 last year and it contained exclusion items on line 27, you can enter the total of these lines here. An exclusion item is permanently nondeductible for AMT purposes, as opposed to a deferral item which will reverse in later years."

The info on Form 6251 line 27 comes from the "Qualified Dividends and Capital Gain Tax Worksheet" line 7

What should really go in the Additional adjustments or preferences treated as Exclusion Items field for 2019? 

Whatever I enter in the Step-by-Step "Other Adjustments Used to Determine Credit" field named "Additional adjustments or preferences treated as Exclusion Items" field ends up on Form 8801 line C2 "Enter any portion of line A8 treated as an exclusion item" as the "Total".  Line A8 is "Form 6251, Line 2h, Qualified small business stock"

Looks like a bug to me

Indeed, the instructions ( https://www.irs.gov/instructions/i8801 ) for form 8801 say the following for Line 2:

"Enter on this line the adjustments and preferences treated as exclusion items. Exclusion items are only the following AMT adjustments and preferences: certain itemized deductions (including any investment interest expense reported on Schedule E), certain tax-exempt interest, depletion, the section 1202 exclusion, the standard deduction, and any other adjustments related to exclusion items. If you didn’t file a Schedule A in 2018, include your 2018 standard deduction. Combine lines 2a, 2b, 2c, 2d, 2g, and 2h of your 2018 Form 6251. Don't include any amount from line 2j of the 2018 Form 6251. Instead, include the exclusion item amount from the Schedule(s) K-1 (Form 1041) you received for 2018. That amount is shown in box 12 with code J. If you included on line 3 of the 2018 Form 6251 any adjustments related to exclusion items, also include those adjustments in the amount you enter on line 2. Enter the total on line 2."

This is why I think the Standard Deduction fits my scenario. Still, it would be nice if TurboTax fixed this bug in their documentation.

I am running into the same problem for this field. If I enter line 27 from Form 6251, it disqualifies me from receiving the AMT credit and actually makes me owe quite a bit of money. Turbotax needs to clear up what should be entered in this field.