Real issue here as you pointed out - is the power supply. Cheapo, weak power supply was a cost cutting measure to be sure.
135W were pretty standard in the day (for a small box at least). Still got a PC-45/III PSU here - admittedly slightly older but it's just 110W.
I'd guess the mainboard with 16 MB RAM is still below 60W, so that'd leave plenty of margin for upgrades.
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Just took a quick measure: A3000/30 + 1 GB HDD + 12 MB ZIP + Merlin Gfx 4 MB + A2065 + Maestro = 97W primary (108W peak, 92W with HDD powered down).