That's not a good power supply to get. If it's linear then it's hugely inefficient, and you don't want 13.8V because there aren't really 13.8V bulbs on the market. 13.8V is designed to run automotive accessories (CB radios, etc) because that's the approx full-charge voltage from a lead-acid battery.
Originally Posted by treddy
Since you're planning on replacing the bulb, using the common 12V or 24V halogen bulbs (e.g. MR16) and power supplies (eBay 400306116935; note that's 220V though) that are used for kitchen lighting is the easiest option. You can buy all of those bits at your local hardware store pretty easily and cheaply, though high power bulbs seem more easily found online (eBay 75W 400331920368 or 100W 290622077567). You'll maybe need to buy an MR16 socket; I don't know what's in the enlarger.
You can also get cheap 12/24V industrial switching supplies that will run halogen bulbs, e.g. eBay 160768220046. You do need to do some mains wiring for those though, which is best avoided by buying an all-in-one switching halogen supply ("electronic transformer" is how they're often branded) designed for lighting that has a cord and plug on it already.