Capacitors tend to deteriorate (sometimes badly) with age. If you connected it straight up, then one or more of the original capacitors may be at or near short circuit, and you could damage the ultra rare one (or few) of a kind item (if it is NOT a fake).
Some types (electrolytic), actually use a small amount of electricity (current) to reform themselves, so an electronics expert, may decide to gradually ramp up the current (by gradually increasing the voltage), and maybe limit the current, so that if it does try to use way too much current, it will not do too much, or hopefully any damage.
The electronics expert may decide that they want to examine the capacitors, for signs of impending damage (e.g. bulging cases, liquid discharges etc).
With a normal, older item, which is not worth very much. The risk of plugging it straight into the power (through an adapter, if necessary), is probably worth it.
But we are talking about something, which could be worth a considerable amount of money. SO it would be a shame to blow it up, and potentially lose unique data contained within its ROM (and similar) chips.
Any custom chips/parts, unique to this prototype, could be virtually impossible to ever replace.