Just googling around, an adult male apparently is worth somewhere between 120k-150k (kilo)calories if they're between 140lb to 180lb. Now just using google's online energy conversion calculator shows that 120k kilocalories is worth almost 140 kilowatt hours. The average US home apparently uses 30 kilowatt hours per day on average, meaning all of the caloric energy in one black person weighing 140lb could power a US home for about 4.5 days. This means if you could extract all of the energy from every black person in the US(41.31m) you'd have have enough energy to power 185.9m~ US homes for a day(to be referenced to as "US home days" further on).
Now you won't actually be able to get all 100% of that caloric energy. Firstly all thermal engines are limited in their efficiency and the most efficient turbines that I've heard of in power plants run at about 65% efficiency. The processing cost of the material will also cut into our energy budget. However, burning flesh directly is not very possible due to the water content. You mentioned a hydraulic press, but I'd argue that it's cheaper and more efficient to use a big blender. After that you can do what some places do with food waste and manure, which is to let it
ferment and collect the methane and other gases that it produces. If we assume 50% of the caloric energy we put into that comes out as burnable gas and then 50% of that energy can be turned into electricity then we'd produce about 46.5m~ US home days of power instead.
It's likely that we'll end up with less than that it terms of power though. Some more fun calculations though: Apparently NYC uses about 11 billion watt hours(11 gigawatt hours) of power a day, so (46.5m x 30k) / 11b = 126.8~ days of electricity to power NYC. Therefore if we started juicing and burning niggers for fuel then we could potentially power NYC for around 126 days in this very optimistic scenario. If we took into account black obesity rates then we may be able to power NYC for even longer.
The added benefit of this method is that you can use the fully fermented fluids as fertilizer after you treat and dilute it. The stickier and more nasty bits won't gunk up any power plants or produce noxious pollutants either.