Instability, maybe a fire, nothing you can't handle.
Fortron Source/Sparkle Power (same company owns both brands) makes good inexpensive power supplies. These are rated at 70% peak load, so a 400W unit should be enough unless you can find something around 450W for a small price increase.
I haven't heard too many complaints, I'd think it would be good for at least 200W continuous power and probably not too much fluxuation so long as your local power grid is "clean".