That's combined total power output for two of the three rails that the PC uses.
12v x 2a = 24w
5v x 10a = 50w
3.3v x 8a = 24.4w
24w + 50w + 24.4w = 98.4w
You're right. It's certainly not 200w as advertised.
And I agree that you should look into a more efficient DC-DC PSU.