The problem is you don't have the adapters so you're missing two pieces of key information, 1 the mA rating and two the polarity of the plug, which are both listed on the power supply adapter. Is it listed anywhere on the units themselves, if it is it'd generally be at the plug in spot. You can get an adapter that can supply more mA as it won't force current into the device, voltage does that the mAh rating is only how much it's possible for the supply to produce, so it needs to be a 4.5 volt supply capable of whatever mA the units draw, if you get a supply that can't produce enough current the voltage may drop and cause them to work improperly, but given what these things are they shouldn't draw more than a few hundred ma of current. The plug polarity is actually a big problem as if you get that wrong even if you have the right voltage it may smoke them, THAT at least should be on the device itself, it's usually right at the power plug in point and will show a ring and a center prong one will be positive the other negative. Typically it's ring negative and pin positive but that's just common not a garuntee. Other than that obviously the plug has to fit.