As you can see the "12V" and "4A" indicator on your picture provided, then usually those universal 12V 4A power adapter should work fine.
Here are some examples of power adapter you may use (proceed at your own risk):
https://shopee.com.my/-READY-STOCK-CCTV-LED...0a-83326af3c265https://shopee.com.my/AC-DC-12V-Power-Adapt...cf-32a191bb077cOr if you want to be "safe", find those Astro installer/technician that sells the Astro branded power adapter for the PVR box model you're using.
Based on the picture, it is PVR box, also known as DMT5.
Based on what you said, it seems to me that this box has not been powered on for more than 1 month, right?
If yes, once you manage to power it on, you will see "please insert correct smart card (S14)" error, and then a while later, you will see "We apologise for the service interruption" message.
If this happens, you'll need to refresh the smartcard first. Just follow the on-screen instructions to send a SMS to refresh the smartcard, or you can install My NJOI app on your phone, enter the smartcard number, and then tap Settings>Refresh Smartcard>REFRESH.
Once it is successfully refreshed, then you'll able to view the channels.
Try to "revive" the PVR box whenever possible first... Because Astro PVR box is considered a "rare item" now

Icic. Thanks a lot for all the useful info.
Maybe I also will search around my house for similar adaptor.
I hope it is not damaged by lightning strike etc. And it is still working but just simply Becos the adaptor is not working.