it may mean a couple of things,
1 you may have an old psu already.
2 if the psu is not that old then it most likely be a low quality one.
be sure to check the specs of your psu, just to be safe. a good 550w psu usually has 2 6-pin
He didn't say it was a 550W psu, he is trying to power a 550 ti graphics card.
Please give us the make, model and wattage of the power supply.