Screen blackout but the system can powered on using battery or adapter

It sounds like the back light power inverter is triggering a safety feature, perhaps due to a fault or bad charging system. I'd first contact Dell to make sure you're using the right power adapter for your unit. Enabling a bios pdu scan that's resulting in a message such as the one you described WARNING: 130WATTS ADAPTER DETECTED, U MUST USE A 210W OR HIGHER ADAPTER" THE PERFORMANCE WILL ADJUST TO MATCH THE POWER OF YOUR ADAPTER" is a hint to a larger problem so, if that's all correct take that to an authorized dealer and swallow the cost. Remember that's a workstation so lifecycle services may be having issues with the brick.

depending on operating system..
go to power management and find screen brightness..
It's separate for battery and AC

If the laptop battery is more than 3 - 4 years old then the battery could be worn out. Rechargeable batteries have a finite number of charge and discharge cycles and will lose their charge capacity over time, i.e. won't charge to 100% and gradually the charge reduces until the battery won't charge up at all. OR The battery shows a 100% charge but when the adapter is disconnected the battery drops off to zero capacity in a very short time. If the battery drops to an unacceptable charge level then the battery needs to be replaced. Rechargeable batteries will fail if stored in a discharged state for long periods.

Whenyou connect the power adapter into the laptop, does the power LED lightup? If not then -The battery adapter or the adapter's power lead or the laptop's powersocket could be faulty.Check power adapter's DCplug that connects into the laptop power socket with a multi-meter, the voltageshould be slightly higher than the voltage that is printed on the label on thebottom of the adapter. If the voltage is zero or way below the voltage that isprinted on the label then the power adapter is faulty and needs to be replaced.If the adapter is OK thenconnect it to the laptop and power it up, then look at the power/batterycharging LED light and wriggle the power plug in the laptop's power socket.If the power/battery LED light flashes and in a certain position this LED lightstays firm, then the power socket is either faulty or it has a dry solder jointwhere it is connected to the motherboard.This can be repaired but itrequires the laptop to be completely dismantled to get at this power socket andrepair. If you cannot DIY then I suggest you get a quote first.

First of all, you need to make sure your power adapter is providing enough power to both run the laptop & charge the battery. A very good way to do this is to compare your laptop voltage & ampere requirements (written on a sticker on the bottom of the laptop) with the voltage & ampere ratings of the power adapter. Voltages should be the same, or the power adapter's voltage about up to 0.5 volts more than the laptop's voltage rating. Amperage of the power adapter should be at least equal to or greater than the laptop's rating. It should never be less than the laptop's rating, or else the power adapter will be providing insufficient amperes to charge the battery. Of course, the power adapter's nominal amperage might be ok, but it degraded on usage. You can verify this by testing using a good or new power adapter.
If the battery did not charge using the new power adapter, take the battery off the laptop, & using a dry tooth brush, scrub in between the fins of the battery connector on the motherboard & on the battery it self, then put the battery back into the laptop & try again.
If this still did not resolve the problem, then the battery itself could be bad. Try it on another laptop, or try a good or new battery in your laptop.
If this did not work, there might be a possibility that the charging circuitry on the laptop's motherboard is defective & needs servicing. In order to do this, the laptop needs to be disassembled & the motherboard checked for defective/burned out components in the area near the DC jack. Any defective/burned out components found should be replaced, or you might need to replace the laptop's motherboard altogether.

Blackout Display Mode: When the Blackout mode is activated, the display turns off to reduce power consumption. The additional power made available by turning off the display helps enhance sound quality. If a button is pressed during the Blackout mode, the display will illuminate for 5 seconds before blacking out again. Blackout Mode On and Off (CDA-9855 only) When Blackout mode is turned on, the display will turn off to reduce power consumption. This additional power enhances the sound quality. Press and hold FUNC. for at least 2 seconds to activate the blackout mode. The display will turn off. • If any button on the unit is pressed during the blackout mode, the function will be displayed for 5 seconds to show the operation before returning to Blackout mode. To cancel Blackout mode, press and hold FUNC. for at least 2 seconds.
Copied from the alpine user manual..
Hope this helps

I have to answer this question with just plain old common sense. Get a new one! This is crazy. If you get a new one, you will have a better, more upto date and something you can handle with todays OS and obviously new batteries. That is too old to mess with. I fixed a powerware once and the plastic was falling apart and the PC board was held together with a rubber band. Not worth it.

Your Battery went bad so you need to replace it.
and if you wanna run through AC power adapter then just take off your battery then plug in your power adapter then turn it on it should be working.

You are simply in blackout mode. This is so at night you aren't blinded by the glow of a screen. Here are instructions right from the manual to turn on or off.

Blackout Mode On and Off
When Blackout mode is turned on, the monitor display will turn off to
reduce power consumption.
This additional power enhances the sound quality.
1 Touch [VISUAL] on the main source screen.
The VISUAL selection screen is displayed.
2 Touch [OFF].
The backlit-display portion goes out.
3 Touch [OFF] again to cancel the display backlight.
• To make the setting, set to “Setting the VISUAL Touch Button” (page
34).
• If any button on the unit is pressed during Blackout mode, the
function will be displayed for 5 seconds to show the operation before
returning to Blackout mode.
• While the backlighting is turned off, the function indicator

you might not have it in a ups power back up plug.