Is there an adapter for plugging a 3-prong plug into 2-hole wall receptors? And is this safe for electronics?

Yes there is but it is less safe since this will now be ungrounded. Look at all of these pics and you will see a common adapter than may reinstate a ground if the outlet box is grounded. You could also install a GFCI outlet but it still isn't grounded. Ungrounded Outlets | Reuben's Home Inspection Blog (http://www.structuretech1.com/blog/tag/ungrounded-outlets/)