Worth the risk?

It will work fine.

Cheers!

AMD recommendations tend to be conservative to account for old or poor quality psu's.
Since the card does not need any auxiliary 6 pin power leads, you should be ok.

it's depend on what is your current psu..

If it true power psu, then go with it, you'll be okay..

but if you run with the fake psu, well...you have to get the real one..

HD 3650 is extremely low power card, even no name PSUs should run it...

       

As Far As I Know..

Even no name computer need a good psu...

i don't think that i should explain why to an expert..  

That's true. But if he bought a card like HD 3650, he must be low on budget. And upgrading the power supply unit on an old system like that would be a little not clever. Sure, for a nice gaming computer good PSU is essential, however, for a computer like that - hardly, it will not consume more than 120 watts.

Since the current psu is working, It will likely continue to do so.
I would not worry about the possibility of some sort of disastrous failure if it is underpowered.
If, by chance the psu is not strong enough,which I doubt, the graphics card simply will not work properly, showing artifacts or the like.
I see no risk in trying it out first.
----------------------bottom line---------------
That, is , after all the question the OP asked.