An apparatus for supplying paint under pressure to a paint applicator, the apparatus comprising: a handheld airless spray gun comprising: a housing; a fluid pump having an outlet disposed within the housing body; and a spray tip assembly fluidly connected to the outlet of the fluid pump and having a spray tip bore for receiving and holding a removable spray tip so that an inlet of the removable spray tip is aligned with and in fluid communication with the outlet of the fluid pump; a spray gun adapter configured to be installed in the bore of the spray tip assembly in place of the spray tip, the spray gun adapter comprising: an adapter body having a lower portion configured to fit in the spray tip bore of the spray tip assembly and an upper portion configured to extend out of the spray tip bore; an adapter bore that extends into the adapter body from the upper portion toward the lower portion; an adapter inlet in fluid communication with the adapter bore and located in a sidewall of the lower portion of the adapter body and positioned to be aligned with and in fluid communication with the outlet of the fluid pump when the lower portion of the adapter body is located in the spray tip bore; and an adapter outlet in fluid communication with the adapter inlet via the adapter bore and located at the upper portion of the adapter. a housing; a fluid pump having an outlet disposed within the housing body; and a spray tip assembly fluidly connected to the outlet of the fluid pump and having a spray tip bore for receiving and holding a removable spray tip so that an inlet of the removable spray tip is aligned with and in fluid communication with the outlet of the fluid pump; a spray gun adapter configured to be installed in the bore of the spray tip assembly in place of the spray tip, the spray gun adapter comprising: an adapter body having a lower portion configured to fit in the spray tip bore of the spray tip assembly and an upper portion configured to extend out of the spray tip bore; an adapter bore that extends into the adapter body from the upper portion toward the lower portion; an adapter inlet in fluid communication with the adapter bore and located in a sidewall of the lower portion of the adapter body and positioned to be aligned with and in fluid communication with the outlet of the fluid pump when the lower portion of the adapter body is located in the spray tip bore; and an adapter outlet in fluid communication with the adapter inlet via the adapter bore and located at the upper portion of the adapter. an adapter body having a lower portion configured to fit in the spray tip bore of the spray tip assembly and an upper portion configured to extend out of the spray tip bore; an adapter bore that extends into the adapter body from the upper portion toward the lower portion; an adapter inlet in fluid communication with the adapter bore and located in a sidewall of the lower portion of the adapter body and positioned to be aligned with and in fluid communication with the outlet of the fluid pump when the lower portion of the adapter body is located in the spray tip bore; and an adapter outlet in fluid communication with the adapter inlet via the adapter bore and located at the upper portion of the adapter.