[Wiglaf]

I know nothing about combining power supplies or your amp draw. However, residential recepticles(US/Canada) can handle 15 amps through the plug and 20 amps pass through on the device. The wiring and breaker is probably 15 amps for all loads on that circuit. The real scary part and what might burn down your home is that loose connections cause tiny little arcs that slowly build up heat which wears away the metal and creates bigger arcs and more heat. The cycle ends when it all finally burns up. You have a much greater chance of a problem with a rats nest of plugs and wires under your desk.
The UK I believe uses 240v(rms) 50Hz. I can't seem to find anything definative on amperage but I think they are rated 250v and either 10 or 20 amps. I am guessing 10 as this would be equivalent to a North American 20 amp recepticle (120v * 20a=240v*10a=2400va)