No, that PSU won't raise your electricity bill, assuming they have the same 80 PLUS efficiency. The system will still use/pull only the maximum wattage required, regardless of whether you have 500 or 850 Watts PSU.
Wattage number is not always important. The quality and the make matters. The main concern is the "quality" of the power, the quality of the components used/CAPS, as well as the total AMP drawn on the +12V RAIL (output), the efficiency under load, "ripple suppression", among other factors.
The total wattage number of any PSU is not always really the most important deciding factor, primary concern is the 'quality' of power it produces, and the total capacity of the 12V source etc.
And no, the extra power won't go wasted, it just won't get fully utilized.
Let me explain------------> If suppose you have a 500W PSU installed on any RIG, then that does not mean that it will always draw the full wattage/500 W.
Nope....... The amount of power drawn is determined by the number of components on that rig/computer, and how much they actually require. The amount of power drawn will only be equal to what is required, and not more.
Suppose, if all the components of a rig require 400 W to run, then the "load" on the PSU will be 400 W, and hence the power draw of that particular PC will always be 400 W (depending on the efficiency obviously), regardless of whether a 500 Watt or a 1000 W PSU is installed. PSU efficiency is a different matter though, as how well the PSU converts the AC power it receives from the outlet, to DC.
Any electricity which is not converted from AC to DC, is given off as heat. A PLATINUM certified PSU might help you save a little on your electricity bill, over a year, though this depends on many other factors as well. Because any high quality Tier 1 platinum certified PSU is rated for at least 90% efficiency at 20% load, 92% at 50% load, and 89% at 100% load (just a rough estimate).