The impact of a voltage source converter-based HVDC (VSC-HVDC) infeed on a line-commutated converter-based HVDC infeed (LCC-HVDC) at the same busbar is investigated. Steady-state aspects such as the maximum available power (MAP) as well as transient aspects such as temporary overvoltage (TOV) and commutation failure immunity index are considered in the analysis. The results show that VSC-HVDC improves the maximum available power, reduces TOV, and makes the LCC-HVDC less susceptible to commutation failure. The resulting improvement in performance of the LCC-HVDC is quantified by a proposed "apparent increase in short circuit ratio" (AISCR) index. AISCR is a measure of the increase in short-circuit ratio for the LCC-HVDC that would be necessary in the absence of the VSC-HVDC link to obtain similar performance. The analytical results are validated by a detailed electromagnetic transient simulation.