I'd keep the two power supplies. The cheap wall wart power supplies usually aren't very consistent in their rating, just because it says 500ma doesn't mean it's good for 500ma of continuous draw. It really depends on the quality of the transformer, some may be okay, others won't. If you switch your fans on and notice the LEDs dim, even momentarily the power supply doesn't have enough headroom to run everything. At best with an underpowered power supply your fans or LEDs will die prematurely, at worst your house will catch on fire. If you want to run everything off of one power supply I'd suggest buying a larger power supply rated for at least 1 amp, they aren't that expensive, chances are you've got one in your junk drawer from an old boom box or an answering machine that will work just fine.