DL2100 Power supply failure - internal or external?

I have a very old DL2100 running two 14 TB drives (RAID1). OS and firmware are up to date. I have been having problems with unexplained shutdowns - both blue lights are off, the device is not accessible from the network, but the green leds on the network ports are flashing normally. Power button does not work. But if I unplug the adapter cord and immediately replace it, the unit wakes up, lots of happy disk noises, and everything is fine… until next time, which could be 2 or 24 hours from now.

So the question is this: is this more likely to be an external adapter problem (except that the network ports are still getting power) or something internal which would require the unit to be replaced?

Follow up: If I need to buy a new unit (say the EX2 Ultra) can I drop the disks in without losing existing data or will they get wiped? If the latter, can I drop in one, copy data from the other using the old unit, and then drop in the second one?

Thanks for any insights.