Check that your appliances are either capable of auto-switching or manually switching between 120VAC (USA) power and 220VAC (European) power, and that their power supplies are capable of operation on either 50 or 60 cycle power. The manufacturer's website (
www.hp.com) or your manuals should include that data.
Devices that need to be manually switched should be checked multiple times for that before being connected to the higher voltage power sources. Devices that cannot be switched must be connected by a TRANSFORMER power converter, not one of those DIODE converters that are only good for lights and hairdryers. Most modern computer power supplies are capable of working with either 50 or 60 cycle AC, but connecting a 110-configured or 110-only device to a 220 supply is going to cause an explosion, fire, or meltdown in the device, assuming the fuse doesn't pop first.
Properly configured devices may be connected directly (with simple prong adaptors) to a local style surge strip. If the locality does not provide a surge strip, knot the cords for at least some surge protection.
