Is it safe to use MR16 12V AC halogen bulb on 12V DC power source as artificial load
It'll work just fine.

Note that a bulb with a cold filament has much lower resistance than hot, thus inrush current at turn-on is quite enormous, like 10x rated current.

No trouble for a 400W PSU, but if you try your "35W" bulb on a 35W PSU, most likely it will have trouble starting up.