01-02-15, 09:35 PM
11.8V when not connected to modem does not mean it'll still be at 11.8v once connected. You need to check it under load. Chances are the voltage would then fall hence modem doesn't work. Unless the modem states on its case what current it draws the only way you can check is to measure it. Presumably its no more than 1 amp since the original adapter was rated for that. 0.8A is probably ok - but there are also plenty of crap (fake) adapters about on Ebay etc that are best avoided.