That connector is for the AC line in. The connector on the board may be marked with one pin L and the other pin N. The black wire should be L ine in, the white wire should be N eutral. Plugging it in backwards - it should be OK. JUST BE AWARE ! - if 2 machines are in arms length of each other and the line and neutrals are swapped/backwards from each other - you risk the chance that one chassis will be hot in reference to the other (or anything that is made of metal and connected to the AC outlet )
You can verify if there is a problem with a DVM (meter) check for AC voltage between the 2 devices on any metal surface to see if you read any AC voltage. PM me if you are concerned. Most power supplies are setup for 110/220 VAC and this should not be a problem, just be aware. (220 VAC has 2 hot lines, no neutral. So the supply would be OK hooked up either way)
These days this is not much of a problem anymore, most appliances have the ground lug and household outlets have them too. Most small appliances and power units are isolated so no ground plug, just the 2 wire plugs. Much safer.
Tony