Hi,
Many modern power devices like the charger have switch mode power supplies and big input power filters with large capacitors across the line. Inrush current can be really high and cause transients that lock things up..
Plugging my laptop power supply in often makes a loud POP and sometimes a spark. Some BIG capacitor across the line.
See if the problem is the same with relay on-off and the units "power switch" on-off. Some units have their own on-off switch located AFTER the line filter capacitors so less inrush current (for THEM..).. You might dig inside and put you relay across their existing on-off switch.
Might be good here to use opto-isolated relays like these: http://goo.gl/Hu1I5
DISCLAIMER: Mentioned stuff from my own shop...