Simply put one conclusion could be that the headroom for spikes is very less with the charger. So whenever there is a spike, say high cpu usage, or usb drive usage etc, there are power issues.
Get the original power supply, your issues should be gone. It will also be cheaper than any further testing or equipment purchase.
Apart from DLNA, it should handle rest easily. Pihole and smb both take very little power. I would suggest you install Open Media Vault, it has options for containers, use that for pi hole. OMV is by far the least hassle option for creating a NAS. For rest you can use its containers. And if you want hassle free working, just get another PI. These are cheap and very reliable.
DLNA should depend on whether it involves any re-encoding/decoding. If it does, you can forget it.
