Yes Wattage does matter it is all connected...  Wattage is calculated as voltage times amperage  or I * V = W (I is amps or current) ... so 5 volts at 2.5 watts is 2.5/5 or 0.5 amps. 

Each Erupter can be measured at 0.5 amps or 2.5 watts...  so 49 Erupters would be 49 * 0.5 = 24.5 amps or 24.5 * 5 Volts = 122.5 Watts...  or you can take 49 * 2.5 watts and also get same 122.5 Watts    So either of your two power supplys would work.. Just don't count on something that says it will do 25 amps to handle them.  Most electronics are at least in the 5% range of going either way.  I would want at least 30 amps or 200 watts to be safe.  Plust 5% of 24.5 amps is something like 1.225 amps.. so that is 25.625 and if your power supply happens to be on the negative side of that equation it is down that 1.225 amps and will burn up.

Isn't electronics and math fun?!?!?!?!?

Naelr